There's a provocative theory out there that much of the OT (especially Deuteronomy) can be read as hygenic prescriptions aimed at reducing the incidence of disease. This would be a rather natural concern for herders, especially if there were many new people entering the area. In fact, the genocidal tendencies of the OT can be traced this way as well.

Anyway, maybe all the sex concerns started out as a way to avoid STDs. In fact, if the proscriptions were helpful as hygenic guides, their survival and success is explained, since any group that adopted them would be healthier and grow faster. Religion as an evolutionary advantage. 

   I want to be "that dildo"

Love me and Use me, again and again ....

yes yes , to be a loved dildo ....

I Spell M A N , I love women ....

It doesn't matter why the behavior crops up, just that it did and was advantageous at the time. Even if the aversion to homosexuality and other sexual rules were just due to a leader's personal insecurities, when some disease swept through and afflicted people who were promiscuous and/or engaging in less hygenic behaviors, the survivors were the ones following whatever ridiculous laundry list of behaviors. So, not only were more people raised hearing about the rules, the survivors had a first-hand account of "god hating those who don't follow them."

If someone started the practice of rubbing garlic on their head because they hallucinated an interaction with an angel, then giant birds appeared and started biting off people's head, but skipped the garlic headed, it doesn't matter why he started applying garlic, just that it is helpful in his environment (one filled with giant head-eating birds.)

 (Sorry, a little rambly.)

-Triften 

Sex is natural and normal behaviour for healthy adults. Most people simply cannot be happy without it. So people are going to have sex, full stop.

The choice of whether to be monogamous or not is a profound lifestyle choice. Most people are ready for sex long before they are ready for monogamy. Pushing people to be monogamous creates more problems than it solves in the form of unhappy liasons leading to cheating, violence, substance abuse, depression and unwanted and abused children, to name a few. The choice of monogamy is too important in people's personal lives to properly be the subject of social pressure.

Cigarettes contain an addictive drug and are marketed aggressively by huge corporations. There is no natural drive to smoke them; the behaviour is learned and often comes from peer pressure and advertising. Quitting smoking is almost always a net benefit to the quitter, socially, physically and emotionally. Yes it is difficult for some people to be happy without cigarettes (and religion) which is why I don't think they should be made illegal. However the certainty of a net benefit to the quitter, and society at large, is sufficient to justify a socialization campaign to discourage the habit.

When you tell people to be monogamous, you are fucking with their whole lives. When you tell people to quit smoking, you are doing them a favour. That's why the former is not OK and the latter is.

Obviously, the best solution would be to invent harmless cigarettes and/or find cures for all the smoking-related diseases. Not sure why the former isn't happening, but I'm pretty sure people are working on the latter. 

Sex does involve risks, and those who engage in it should be responsible. Yet in keeping with the OP, I don't think the abrahamic god would approve of homosexuals even if they were responsible and monogamous, or even monogamous heterosexuals if they were doing something other than missionary.  Even auto-eroticism is admonished, which does not cause STD (unless calluses qualify).

 As an aside:  Smoking can affect others than the individuals engaging in it.  To the best of my knowledge, there is no such thing as secondhand sex (pun possibly intended).

But this is STILL all subjective. What type of empirical procedure can be applied to answering the question "which forms of human sexual behavior result in the most advantageous social outcomes?"?

DUH. People like to fuck. But if I start fucking the ladies at work it's going to create problems both at work AND in my marraige. The animal in me says have at it. Spread my genetic material. But the rational part of me recognizes that spreading my genes willy nilly may both feel really good and propogate my genome, but the social consequences of this behavior will be decidely negative. There is NO evidence that a modern technological society is bettter or worse by having a liberal sexual morality. It is conjecture to assume an answer one way or the other. And laying this at the feet of up tight religious conservatives is a dodge. Just ask a lesbian how she feels when her partner jumps in the sack with somebody else. And, BTW, I never suggested that monagamy should be forced on anyone. 

That isn't even hard. We have social indicators and we have survey techniques that can reveal sexual behaviour. Should just be a matter of doing a huge, cross-cultural sociology study. 

The problem is, human sexual behaviour is pretty much the same everywhere. It is the cultural customs that differ, but never manage to make much of a dent in the hardwired behaviour anyway. So the study probably wouldn't tell us anything we don't already know.  

I think if we look at the social indicators in countries with relatively liberal ideas about sex versus the indicators in countries with more repressive ideas, we will see pretty quickly which cultural millieu creates the healthier populations.

Actually, this is not true. The animal in you wants to seek out and establish a long-term mating relationship with one main partner. That's hardwired human behaviour.

See above.

I don't lay it at the feet of anyone. All I have been saying is that attempting to control people's sexual behaviour is much more problematic, practically and ethically, than trying to control smoking. It is partly the failed attempts of uptight religious conservatives that has taught me that.