At a time (thousands of years ago) when those "Gods" were invented, your tribe's survival depended on a strong population with genetic diversity. Obviously, the rulers and law makers of the time had figured out that too much inbreeding wouldn't be such a good idea and could lead to (insert your favourite: Tasmania, Europe's Royalty, ...). Hence they permitted their men to raid neighbouring tribes and take women as prisoners and sex slaves. (Read it up in the Pentateuch.) Wasting some good strong semen up another man was counter-productive, hence forbidden and sinful. The Rulers didn't care how a guy felt, whether a woman enjoyed being bred, or whether a member of the tribe would have preferred to live with a same-sex partner. Such behaviour was a waste of scarce resources that wouldn't add to the variety of the tribe's gene pool, therefore it was Sin. Better to set an example and lose a few deviants (by stoning) than to allow a larger number to disobey "God's Commandments".
The thing that irks me in this day and age is the fact that Earth is suffering a massive problem of overpopulation, yet we stick to those ancient tribal rites that only exacerbate the problem. Muslims insist they have to outbreed Infidels. Upholders of "our Great Western Christian Culture" lament the threat of being outbred and want to prevent any of their "perfectly good sperm" being wasted. And all of that in the name of some fictitious Superman who allegedly created mankind in his image.
If that were true, and this all-powerful, all-knowing, all-loving mythical figure had made men and women: Why did he make some of them gay? Why didn't he simply give every man the right hormonal balance to be attracted to women - ideally only to the one (or four) allotted to him? And vice-versa?
Making some gay, some lesbian, some even more confused, when you could avoid all the pain and heartache, not to mention jealousy and violence and coveting, seems like a cruel hoax to me and doesn't comply with the "all-loving" attribute. It's what one would rather expect from a sadistic creator, with a touch of masochism thrown in, considering he is said to have returned to get himself killed for getting it wrong. Why not plan ahead and get it right the first time!
As Heinlein put it: "A rather sloppy way to run a Universe..."