Humans live outside of Nature. In fact, Nature can get along better without Humans than Humans can without Nature. Even if you want to disregard these things, just consider that sex for procreation or recreation is a purely Human attribute. There's no other species around who has the intelligence to figure out that having sex makes babies or is something fun to do on an otherwise boring Friday night. Not to mention that there is plenty of evidence that bisexuality is displayed in many mammalian species.
Humans are the only ones who deny it.
Second is the violation of Family Values. This argument is perhaps the most vague and devoid of definition. My parents have been married since 1954 with only military service causing any separations. I'm sorry, but this Family Values reason is just ludicrous. This brings us to God forbids it .