Frankly, the reason anti-gays are almost entirely religious, is that practically the only way to reach the conclusion gay sex is sinful is to believe that anything can be morally wrong which does not hurt someone else. For that, you need to declare "objective morality." Funny thing about that objective morality, religious types differ widely over time, place, and religious brand, over just what that objective morality might be. Perhaps for the same reason they differ so widely over what god might be, --- that is because neither objective morality or god exists.
If there is a god, I want to believe that there is a god. If there is not a god, I want to believe that there is no god.