Religion and sexual orientation is both part of a person's most inner being. It's part of what makes people who they are. How they became like that is a bit of a red herring, it doesn't matter, that's who they are now. Just because they made a choice to become a muslim at some point during their life doesn't invalidate their thoughts and feelings towards a particular subject and it certainly doesn't make you any less of a jerk to mock them.
I guess I'll head over to that other thread now.