I have the right to say just about anything I want. If I want to say "Riddler, Riddler, jew niger" I can. Of course, there would be consequences for saying that in certain situations, but it wouldn't be illegal. Saying "oh my god" is an expression similar to "loving stuff." When I say "loving stuff" I don't literally mean that I'm having love with stuff, it's an explanation. Likewise, saying "oh my god" doesn't imply I believe in god, because it is an exclamation.