Isn't religion a choice? Being a certain skin color is not. I doubt most handicapped persons chose their condition, either.
Being straight or gay is maybe a choice (I'm uncertain whether any genes have been specifically IDed yet.).
There's a big difference between *choosing* a path in life and being born into one. It's perfectly fine to discriminate against people for choices they make. It's not ok to discriminate based on their lot in life.
I'm saying that as a pretty liberal guy, too. I just don't like legislation forcing me to accept some people's choices. If they choose, they can deal with the consequences.