Of course we might expect religions to take issues about sexual life and conduct seriously (though with some due sense of proportion, compared with other matters, like issues of social justice -- and it is the seemingly too prevalent lack of that sense of proportion that prompted my passing remark). What is quite bizarre is the kind of daft obsession that leads the Anglican communion to point of breaking up over the question of gay bishops. And what is simply vile is the kind of lunatic obsession that gets women stoned for adultery.
The statistical norm might be defined by what is true of the majority. But why on earth would we want to define the moral norm solely in terms of what the majority of people do? That would mean that, by definition, vegetarianism, atheism, and marriage between different races was wrong. It would mean that you were morally wrong if you were an abolitionist in the South or fought for equality for women in America in the early 20th century (I'm not sure when that became the majority position) or fight for equality for women in many countries today. For that matter, it would make it wrong to be a Jew or a man who goes to college or a firefighter.
Perhaps what you mean is that homosexuality could be considered biologically "non-normal" (it's not clear exactly what that might mean, since whatever we do is allowed by our biology). That may not be true, depending on what one means by biologically normal. But even if it were, it would not make it morally wrong, since lots of biologically "non-normal" behaviors may be moral, including, for instance, monogamy and vegetarianism.
Lack of consent isn't the only argument, but I doubt that anyone ever thought it was. Roughly, we think we need consent when we think the person might reasonably object if they only knew about or understood what was being done to them. In the case of pedophilia, there's plenty of reason to think that the child would object if s/he understood. As it happens, I know someone very well who was the victim of a pedophile. When it happened (and it happened more than once), she didn't understand; she was four years old. But if you asked her about it now, she would say that what this man did to her was very wrong and caused her a great deal of torment as she came to terms with it.
Though it's hardly the whole story, the phrase "taking advantage of" is entirely apt here.. This man didn't have that young girl's good in mind. He was using her for his own disagreeable reasons. It's a straightforward case of what Kant would call using someone as a mere means. Offhand, I can't think of any cases where that's okay.
A footnote to Peter Fosl's sensible response.
The trouble, of course, is in the talk of 'non-coercive' incest. Where different generations are concerned -- father and adult daughter, for example -- it would be naive to suppose that the younger party, who may think she is freely consenting, isn't in many cases subject to subtle coercion. And even if, leaving the issue of potential offspring out of it, there is nothing morally wrong with genuinely non-coercive incestuous relations between adults, it could well still be a bad thing if people generally believed that to be so (for the belief, by relaxing the received taboo, could have the bad effect of creating a context in which subtly coercive incestuous relations become very much more common).
This is an interesting phenomenon in moral thought more generally, it seems. There can be cases where it might be permissible to do X but it would be a bad thing if people (including ourselves) generally thought it is permissible to do X -- e.g. because we just can't be sufficiently trusted to judge when something is a case of X of the permissible sort. Think about e.g. examples where doing X involves acts of euthanasia.
Back to incest: there however surely can be genuinely non-coercive cases. For example, the brother and sister separated near birth, brought up by different adoptive families, who later meet and -- ignorant of their blood relationship -- start sexual relations. It happens. Their initial incestuous relationship surely didn't involve any wrong-doing on their part. And what if they continue, after the discovery, in a knowingly incestuous relationship (though, now appreciating the genetic dangers, abandoning plans to have children together)? I can see no decisive reason for supposing that this is wrong, or indeed for supposing that there is a danger in thinking this sort of really rather special case of an incestuous relationship isn't wrong.
Here are some philosophical questions that I happen to be interested in (or have been interested in, in the past). "Are beliefs functional states?", "What makes our knowledge of our mental states particularly authoritative (if it is)?", "What is the best formulation of a causal theory of reference?", "How much mathematical knowledge can usefully be thought of as logical knowledge?", "Can one give a cogent neoHumean account of the notion of a scientific law?". And there's lots more where they came from -- all highly abstract conceptual questions. And in engaging with these very abstract questions (just as with mathematicians or scientists engaging with their abstract questions), I'm a very long way indeed from dealing with anything that engages with my sexuality. So surprise, surprise, you won't learn anything much about that from reading what I've written on those topics. Sexuality just doesn't come into it.
And so it is with an great deal of what is written by a great number of philosophers. It would be absurd to say we "present ourselves as asexual"; it's just that our topics have nothing whatsoever to do with sex. (I suppose if you are some kind of dingbat Freudian, you might speculate that we reveal something about our sexuality by the very fact that such abstract matters fascinate us. But common observation suggests quite otherwise. Looking round my philosophical acquaintance, puritans and libertines, straight and gay, romantics and party people, it seems we are quite as sexually diverse as the rest of the population)
However, there is also of course a good deal written by many philosophers that does engage with less abstract, more immediately human, concerns. And here too it would be absurd to sweepingly say that philosophers "present themselves as asexual". How could that be said, to take just one example, of a writer like Martha Nussbaum?
Ignore that typical Derridian silliness. When the topic -- as it is with a lot of philosophy -- is quite remote from anything to do with sexuality, of course philosophers trying to get at the truth about it typically do so without "presenting themselves" as sexual beings. And when the topic -- as it is with a lot of other philosophy -- is more closely bound up with the human world, then there are plenty of philosophers who do write in a way that is appropriately more personally coloured.
I don't think the illegality of prostitution has direct implications for whether or not we think pleasure is a moral good. We might think that pleasure is a moral good, but might ban an activity that promotes short term pleasure because we think (rightly or wrongly) that it results in a long term overall reduction in pleasure. So, even a group of hedonist utilitarians might ban prostitution if they think (correctly or incorrectly) that it spreads STDs too much (including deadly STDs) thereby producing a net decrease in overall long term pleasure.
Someone might also be in favor of banning prostitution because they think pleasure is of genuine worth, but merely of less worth than other goods (virtue, stable family relationships, etc.). You may also recall that Mill's version of utilitarianism weighs the 'quality' of pleasure and not just the 'quantity'. So, someone might think (correctly or incorrectly) that physical pleasure is of a lower quality than other pleasures and therefore should be weighed less.
I think the very complex pattern of the worldwide laws (and lack of laws) concerning prostitution does not fit the explanation offered by Nicholas Smith. If you look at the information concerning the legality of prostitution in 100 different countries at: http://prostitution.procon.org/view.resource.php?resourceID=000772 you will see that there prostitution is illegal in places that have never even had a widespread religious concept of 'sin' such as China, India, North Korea, and Thailand. At the same time, it is legal in many places where a high percentage of people identify themselves with traditional religions that view prostitution as 'sinful/religiously unacceptable' including Turkey, Italy, Poland, and Greece (though perhaps, high religious identification in these places does not entail that people think it is appropriate to legally enforce the morals of these religions). In any case, I think a better explanation for why prostitution is illegal in such a strange assortment of places (and not in others) depends on whether or not people judge it to be causing unacceptable harm. For example, despite the complete lack of anything like 'puritanical motivations' in Thailand, it is not difficult for people to see that the widespread prostitution there has harmed lots of people (such as women involuntarily trapped in the 'sex-trade') and has been responsible for spreading a lot of disease. Perhaps, even the religious values that often motivate attitudes against prostitution are ultimately grounded in the belief that it harms individuals and society in a tangible way.
Even if both parties benefit from the transaction (relative to the baseline where they do not interact), the transaction can still be immoral. An extreme example would be a mother in Cambodia who works as a prostitute to feed her children. She prefers serving the customer and receiving the money over not interacting with him. And he prefers the transaction over not interacting with her (it only costs him as much as he earns in 20 minutes back home). But it may still be immoral to take advantage of the woman's situation by paying her so little.
Let's leave this sort of case aside and consider prostitution involving two people who are both well off and roughly equally well off -- perhaps a business person buying sex from a college student from an affluent family who is saving up to buy a flashier car. In this case, I'd agree that the transaction is not immoral, assuming free and informed consent on both sides ("informed" meaning among other things that neither has failed to disclose any infectious disease to the other).
Still, this sort of relationship is generally not part of the best life that a human being is capable of. Either person might aspire to a more ambitious romantic relationship in which they would share not only sex but also conversation, literature, travel, sports, emotions, and daily joys, curiosities and sorrows. Where these other possibilities are available but passed up in favor of prostitution, people are falling short of their potential in much the same way as they do when they pass up good novels for trashy ones, news analysis for daytime TV, or evening discussions for excessive alcohol. That's not immoral, so long as no one else gets hurt, but it's still ethically questionable in a broad sense of ethics as one can find in the ancients and in Bernard Williams, for example.
Kant emphasized what he called the "categorical imperative," for which he gave two formulations. The formulation that seems most plainly to apply here is that we should be able to universalize into a maxim whatever decision we make in individual moral decisions. In this case, the question is whether we would be willing to universalize into a maxim that the policy of the military sshould be "don't ask, don't tell" for anyone of any gender and any sexuality. But it seems that we do not have such a policy for heterosexuals, and as far as I can tell, no one would think that such a policy would sensibly apply to heterosexuals. So it sseems we cannot universalize this policy, in which case the policy looks, on Kantian grounds, to be prejudicial.
Let's see if I'm understanding. You hook up with someone whom you really like and who really likes you. There's a considerable sexual attraction. The hormones are more than buzzing and you are of an age when it is only too natural to want to start a sex life (and you are old enough for it to be legal). She is more than willing and is sending all the right signals. You fancy her like mad. And wow, it happens!
Erm, well excuse me if I don't see your problem! Rash? Well, what is life without a few rash adventures along the way?
But actually this wasn't particularly rash (unless zero contraceptive precautions were in use)! Just unplanned, but still mutually wanted and enjoyed. But that makes it sound to me a pretty good way to get things started, compared with the usual alternatives. Not weeks/months of old-style (or not so old-style) stressed fumblings towards "going all the way". Not some regrettable anonymous shag with a half-willing very drunk girl at a party. Just a happy experience with someone you instantly felt a real connection with. Sounds to me that you should be grateful for that, not anxious or conflicted.
Though you can learn a useful lesson along the way. Sexual attractions have their own dynamics that aren't so easily corralled by thoughtful plans or shaped by philosophical principles. But, hey, that's life!
Isn't this far too like e.g. the question "Is enjoying pornography immoral?" In that case it all depends what exactly is in question: a bald yes/no answer would be hopelessly insensitive to the great variety of materials that fall under the very sweeping term "pornography".
My impression -- and I hasten to cheerfully admit to lack of expertise! -- is that "BDSM" is similarly used as a pretty sweeping term that also can be, and has been, applied to a pretty wide variety of activities. So here too, a bald yes/no answer is surely likely to be inappropriate. Moral philosophers will need to know quite a bit more about just which sorts of activities in what sorts of contexts are up for evaluation before they can proceed to say anything sensible.