Why is homosexuality 'evil'?

I don't think christians believe an attraction to the same sex is evil, just the physical act is. And that is just one of the many things on the evil list of a stupid archaic religion. The reason why I think the bible was written to condemn homosexuality is because many straight men have an aversion to gay people. Somewhat like an aversion to something gross or an insect. They just instinctively don't want to be near it. I also believe there is a biological basis to this aversion. So we mustn't blame them too much, but it isn't too much to ask of a sentient species to try to use intellect over instinct.