I haven't had a run-in with anyone like that outside of political debates and fanfic. Considering I'm applying for jobs as a children's librarian, though, it's only a matter of time (but at least the paperwork scares off a good chunk of would-be book challengers).
Just try to ignore 'em, be politely calm and reasonable if you can't, and if they won't leave you alone get numbers on your side. The way I--in my borderline agnosticism--see it, if there is a deity and they care about humans, why wouldn't they want us to be happy if the cause of our happiness isn't harmful to other people? I get that it's not so cut and dry for a lot of people, but if everyone thought the same way the world would be incredibly dull.
MESSAGE ME IF YOU ADD. I've got a steel safari: Mawile, Clefki, and Forretress. My code's 3136-6781-4024