As long as you are targeting their backwards worldview, and not them or anyone they care about, I guess it's fair game. People get really defensive though, so sometimes you're better off just asking people how they got there so you can watch them dig themselves into their own hole. Hopefully, they'll be introspective and try to self improve; plenty of people are capable of it. If somebody can't defend their worldview, but they don't feel attacked in the process, a lot of people can self correct, even if not as far as you'd like to go.