Whenever you hear the religious say that homosexuality is a "choice" or a "temptation" that people should resist with god's help, simply say:
"There is a name for people who think homosexuality is a choice; they're called bisexuals."
You can follow it up with:
"Of course, that's not always accurate, sometimes they're just repressed, closeted homosexuals."
Non-believers often wonder why the religious are so obsessed with homosexuality. I suspect it is because many of them are desperately fighting the "temptation". They can't stop themselves unless they convince themselves that it is an evil sin forbidden to everyone. That would explain why they implicitly assume that we are all fighting this "temptation" and that gays and bisexuals are simply craven hedonists who have given in to temptation. They can't seem to comprehend that some people are inclined to these activities and some people aren't.
At the same time, it is clear that many of the religious are simply stuck in an infantile state of moral and emotional development where echoing the words and values of the "authority figures" (god or the clergy) seems necessary to be "moral" as they understand the meaning of that term. I suspect that for many religious people their homophobia results from a combination of these two motives. These suggested replies should have the effect of countering the "moral choice" argument, the infantile morality will have to wait for a later post.