If that was true, you should see significant differences between religions. And at the same time very little differences within religions.
Not following you. The Decalogue exists in Judaism, Christianity and in Islam. The Decalogue, and marriage, are indeed extremely recent social constructs.
I'm not promoting religion - I despise any form of it. I merely posit religion as being the source of humanity's prudishness (something the rest of nature does not share).
"I merely posit religion as being the source of humanity's prudishness (something the rest of nature does not share)."
Nature as a whole may not, but there are species even more monogamous than we are out there. I've sort of played a game of "construct an even remotely sensible sexual strategy no species uses" and so far I've come up empty; everything you can think of, including the closest equivalent to "prudishness", is used out there.
On that note, the "missing link" for you is probably that sex and reproduction are inextricably linked for all non-humans, and for all humans up until very recently. Hangups about sex are not hangups about sex; to put it in quite atheistic terms, they are hangups about whose selfish genes get to win out over whose. Start looking at it that way and it makes a lot more sense than your current model, probably.
Our current reproductive strategies are currently in total chaos because of the extremely recent introduction of effective birth control and I see little reason to believe that we have found the best response to that in what is still effectively just one generation, nor that our current responses will be stable over the generations, because the shock is simply too recent in generational terms. (Not to mention all the near-in-generational-term shocks that may be yet to come, including but not limited to: Effective male-directed birth control, effective sex robots for males, technology to permit cloning without loss, technology to edit genes in eggs or sperm, technology to permit taking children to term out of a biological womb, and in the craziest case, technology to completely digitize people and make biology essentially irrelevant.) In particular, it does not seem particularly clear to me that the idea that "sex is 100% just sex and nobody should be ashamed about anything as long as it is consensual" is going to win out, because that crowd tends to use birth control of one form or another, and therefore, in the next several generations can be expected to be bred out. By some definitions of morality it may well be moral, but it won't be stable.
Not following you. The Decalogue exists in Judaism, Christianity and in Islam. The Decalogue, and marriage, are indeed extremely recent social constructs.
I'm not promoting religion - I despise any form of it. I merely posit religion as being the source of humanity's prudishness (something the rest of nature does not share).