Perhaps we should take things right back to the beginning and build from there..?
There was a bang, and a lot of energy got very energetic all of a sudden. It wasn't too happy about this. It decided to do something about it - all the concentrated energy in this baby universe decided to evolve toward a state of inert uniformity. Entropy. It came up with some ingenious ways to do this. Planets for example, suns. All wonderful ways to spread useful energy around in a thin layer of useless heat. And Life. In a large enough support medium, any event that does not contravene the extant physical laws inherrant to that medium, becomes inevitable. Amino-acids form spontaneously in-vitro, if the right chemical pre-cursors and conditions prevail. And later, replicators, DNA strands, single-celled lifeforms... And much much later - Us. Each wiggle and thrash of lifes' fledgling limbs and pseudopods adding a little more entropy to the pile. Complexity out of simplicity, bought at the price of increasing heat-death that much faster.
Life has only one prime-directive: To create more life.
To facillitate this end, it has two fundamentals precepts:
1) Self-preservation.
2) Reproduction.
It has no quality. It has no direction. It has no morality. It does not care about getting better, it does not know what better is. Evolution is just what happens to it when it interacts with the external world. Life creates life. End of story. Then life invented sex. And things got, quite literally, sticky.
Two sexes arose, and life got a drive to have sex, sex, sex, some sex, and after a break for its snackfood of choice, some more sex.
Sometimes however, life gets the whole sex business a little mixed up. Male has sex with male, female with female, and all the rest of our sexual predillictions.
This is because life's little programmers, genes, are very close mouthed "need to know" types. They give their progeny only the absolute instincts necessary to facillitate the 2 defining precepts. But that is all they are told. It is all they are born knowing. Any particular mind, animal or human, gets into the fleshy vehicle it is given, and instinctively knows how to use it. You don't have to learn how to breathe, but you can learn how to control it. You don't need to know how to send a nerve impulse to your muscles, but you get more refined in your movements with practice. You don't need to know how to get an errection. It just happens, usually in the presence of a naked lady, sometimes for absolutely no reason at all, on a bus.
For procreation to happen, there is no reason for us to instinctively know that sex leads to babies. Only for us to have an innate drive to have sex.
Indeed, a gene with coded instinctive 'knowledge' concerning the link between sex and babies would be at best redundant, as the sex drive ensures it will happen anyway, wether the lifeform concerned has the gene or not, and for evolution, minimalism is always the way to go, less is always more, if the same degree of efficiency can be achieved. Baggage hampers, baggage slows you down, however minutely, in a long enough time span, significance arises. A gene which carries redundant information would not be automatically conserved, and so would tend to die away.
And at worst, such a gene would be restrictive, non-promotional of sex. Think of it from the female POV: A gene which says by anology:
"Hey girl, would you like a cookie..? This cookie is a special cookie, eat it, and for a few minutes you will feel as if you've gone to heaven. Beware girlfriend, before you bite, of the side effect: After you've finished eating, and returned to Earth, your whole body and its chemistry will go through 9 months of upheaval, and for the last 2-3 of those months, you'll be near-incapacitated, and extremely vunerable. And finally, you will go through a period of agony as intense as anything you will ever experience, short of death, which, by the way, may well be the result. But on the other hand, you will produce another cookie-maker in the process... Now, wanna cookie..?"
A useful gene..?
No wonder then, if you could ask a primitive human where those little humans come from and why, and he'll say, "Well my woman just keeps making the damn things..." He's a smart chap, the penny will probably drop later on, but instictively-speaking, he hasn't a clue. It's better for him not too.
As far as life's concerned, sex is what matters, and babies are just what happen after. Sex has no conscious intent or purpose beyond the generation of pleasure and the fulfilment of need. It just is. Love is what creates the psycholgical link that exists before and after the event of sex, and goes some way to ensuring the survival of the infant by bonding parents and child in a triangulation of support. But love is another story. Love and sex are usually concurrent, but not necessarily so.
Life existed before it became so self aware as to be able to question its actions consciously. It was still driven to have sex. Life existed before the concepts of right and wrong were invented. It was still driven to have sex.
The sex drive pre-empts morality.
Sex is 'dirty', but we do it anyway. To not do it is to deny our basic humanity, our basic tenent of being a form of life. Life without sex is no life at all. Whatever form of sex you are driven to explore.
Life is sex.
Ask a gun if killing is ethically wrong, immoral, and if it could speak, it would say...
"But I'm a gun... I facillitate killing. It's... What I do."
"But killing is wrong..!"
"But, but, it's my function... My reason for being... I can't do anything else... I have... No choice."
And neither do we. Sometimes our choice of target is out of our hands. But we fire anyway. We have to, we are driven to. It's what defines us. No morality involved, morality comes after we come.
One must approach sex from the tangent of the animal, the evolutionary, the language of benefit to life plural. To approach it from rationality, is to talk about diets to a cheetah, you can impose a diet forcably sure, but don't expect him to go on one voluntarily.
Using this approach makes explaining the why's and how's of mankinds views of the more 'perverse' sexual practices have formed, and are now changing. (I use 'perverse' loosely, evolutionarily speaking, perversion does not exist, only what works, and what does not, in promoting life plural.)
For example: Homosexuality...
Very simply. In expanding populations, with enough resources, a shortish natural lifespan and the resultant high turnover of generations, a group with a high proportion of homosexuality, wether gene-led or meme-led, will tend to increase in numbers at a slower rate than a group which is more rigidly heterosexual. And therefore be at a numerical disadvantage in conflicts over territory and what have you.
In only this situation, is homosexuality a distinct liability with regard to group survival. And wether you like it or not, our basis for defining moral and immoral actions is deeply rooted in this concept. Our ideas of 'right action' and 'wrong action' well from the basic instinct to survive on an individual level, in the furtherence of your personal genetic line, leading naturally to the group level, because your group supports and protects you just as you do it. What is good for the group, what is good for its prolification, is good for you. Anything, any trait, any behavioural preference or prediliction that goes against group survival or numerical advantage, group coherrence or stability must become deemed 'immoral'. It's a self-fulfilling prophecy, because the group that deems immoral these things (homosexuality amongst them) and forbids them, will prosper and dominate, and in doing so, eliminate other systems of morality as the adherrents to these moral systems are physically killed in conflict or begin to emulate what they see as a winning social strategy. Other moral systems must either get on the bandwagon or be crushed by it.
I'm not going to argue God's existance. But religion, the visible facet of the God concept, is man-made. A priest is also a man. He puts words that humans can understand into God's mouth. God says: "Go forth and multiply." To further this tenent, it is no surprise that the priest says, "a sodomite is an abomination against God". He has to, otherwise his group dwindles, and his version of God, (which he may have sublimated into his sex-drive, if his religion bans his actual chance of physical sexuality or procreation), dies with it.
But now our groups, our nations, have reached near-maximal proportions in the stable countries of the West, and in conflict, it is technology, rather than brute population that is the main effector. Beyond catastrophy, the survival of the group en toto is assured. ie: the ancient foundation for a bias against homosexuality has crumbled. We have 'gone forth' we have 'multiplied'. Mission accomplished Mr. God, sir.
Indeed, further multiplication will soon if not already become a factor detrimental to the well-being of the group.
And yet, love and sex remain as important human drives as ever. The satiation of human sexuality is a requirement fundamental to the stability and coherrence of the host society. Sexual frustration, wether homo or hetero, leads to acts of desperation, acts that break the consensual agreements of conduct and society's common criminal penalties, as one drive - the drive to sexual satisfaction overcomes a lesser drive, the drive to social conformity. Frustration --> factions and conflict --> unstable society --> readjustment of society's 'morals' --> Fulfilment --> stabilized society --> prosperous society.
Homosexuality as an inheritable genetic proness, is conserved within the genome, as it does not conclusively pre-empt procreation. Like any other behavior with a joy-buzzer at the end, it can be learned. It can also occur by accidental disruption of hormone levels within the foetus at the 6 week stage resulting in a 'female-type' brain in a male body. Homosexuality is a given within any society of humans. It cannot be 'stamped out'.
It does not matter that homosexual sex cannot lead to children, the conscious/subconscious mind, where sexual proclivity resides, may know this, but the body does not. As far as the body is concerned, pushing your penis into warm cosy cove, be it an anus or a vagina, is always a good idea. Sexual pleasure and procreation, have always been entwined. The body makes no distinction. There is no innate knowledge of the connection between sex and offspring.
"Go forth and multiply" only works when there is somewhere to "go forth" to. When the edge of the boundary is reached, it becomes "Stay put and stabillize."
Hence, the maximal population society which continues to deem homosexuality 'immoral' can only self-generate its own instability, and detriment. A pissed off gay with a gun can create just as much havoc as a pissed off hetero with a gun. The maximal society that is more tolerant to its fringe elements, within reason, will fair better.
Consensual Homosexuality loses its social stigma.
But does this also open the door for other, more overtly 'evil' sexual practices..? pedophillia for example, by linking sex only to the beast inside, will we allow all forms of 'sex' to run wild and rough shod, even over our children..?
Anyway, why is child-molestation so abhorrent..? Worse than rape, worse than murder..? Damage to the child, psychological or physical..? No, for evolution a sexually immature creature has no impact until it has shown itself able to reach maturity, and re-produce, that such damage occurs is true, but it cannot be the basis for a species-wide aversion.
Simply Pedophilla is evolutionarily/socially stupid. It's an immense (shared) risk for the momentary gain of (individual) pleasure. It's behavior almost certain to get you (and your genetic kin) killed.
A progression of 'sins':
*You trespass on my territory, I and my clan may welcome you, give you shelter and food. Or, if you catch us on a very bad day or you act disrespectfully, we may cut off your head and stick it on a post.
(A compulsive trespasser is a danger, mainly to himself, and a liability to his 'parent' group, in that he risks a small but increasing possibility of starting a conflict over territory.)
* Theft: You steal my cow. That was my cow, I fed it, raised it, looked after it, I invested my energy in it. It was mine. If I have a whole lot of cows, I may well give up on you after a bit of searching. If I have few cows, I'm likely to hunt you down and hang your thief ass from the nearest pole and use you as a scarecrow.
(A compulsive thief is a major risk to himself, and quite a risk to his 'parent' group, in that he runs the risk of revenge attacks on the possessions of his group.)
*You rape/kidnap a woman of my clan. She was ours, we had a great investment in her, she was under our protection. Her virginity, fertility and prospects for bonding with another were our assets. You took her, without our permission. You took her without paying us due tribute for our investments. You took her without extending your protection to her, and so relieving us of our duty. Depending on her age, beauty, 'marital' status and usefulness to our group we will expend varying degrees of effort in finding you and killing you slowly.
(A compulsive rapist is very likely to die early on in his career, and think Helen of Troy on a small scale, very likely to embroil his 'parent' group in major conflict. ie: Having a rapist in your group is bad for that group, and killing him yourselves before he gets you all into trouble is a good idea.)
*You rape my child. You hurt my child. You kill my child. My child is my most precious possession. It carries half my genes, it carries my legacy, it carries my only chance of something approaching immortality. Even more compelling than my drive to have sex, is my drive to protect my offspring, and the lives of my future offspring by removing any threat. Ergo: You are dead. And such is my outrage and grief, I will tar your entire genetic strain with the same brush of potential pedophillia, hunt down your family and friends and slaughter them all like cattle.
(A compulsive child-molester is a walking dead man. The family of a child-molester are living on borrowed time. The friends and associates of a child-molester are at serious risk. The only thing to do that makes any kind of social sense with a child-molester in a group is for that group to kill him, before his actions get them killed too.)
Natural law. Morals arising from group survival. Irrational behavior carrying no benefits, for extreme (shared) risk -> Immoral. Evil. Bad.
Of course now we don't really have to worry about these things. Retribution and revenge have been co-opted in the intrests of social stability by the state. The shared group risks of individual actions have been difused. Did anything happen to the wife and family of the Yorkshire Ripper..? Beyond a little social consequence..? A few less invitations to dinner..? Nope.
Only the extremely emotive crimes of rape, and child-rape will tempt a return to vigilantism, someone hurts a child, and the first reaction of even unrelated people, is to howl for revenge, think then, of the terrible instinctual tides of retribution occuring within the body and mind of the parent. But of course, the police, the guardians of social stability, will and must stop them from running amok. Seeing that the satisfaction of this revenge will only destabillize the group en-masse. lowering everyone's chances of survival.
No big surprise then, that slowly and timidly, the snakes begin to raise themselves from the dirt, and whisper that maybe it isn't so bad afterall.
Pedophillia, is a perversion in that it decreases the chances of survival of the exhibitor of such behavior, and his bloodline. All else is just modern-day intellectual frippery.
Homosexuality within a group large enough not to need to breed excessively to better it's chances of survival, is tolerable, and if it increases the social cohesiveness of that group, to be promoted.
Pedophillia can only cause dissention, retribution and instability within how ever large a group. And is to be abhorred. Now, then and always.
In conclusion, I hope I have shown that sexuality, despite being amoral with regard to human conscious rationality, and impossible to adequately judge or justify simply by this method, is not without its stopgaps and checks, it is policed by an older, more organic process, that of group dynamics and survival. There is an inevitability to sexuality that precedes and pre-empts human morality, and it will continue to do so, until we cease to be mortal, and evolutionary forces lose their grip.