So perhaps you should qualify what you mean by "discriminate" in more specific terms.
I don't have any problem with a business that chooses not to involve itself in gay marriage, as many have legitimate religious reasons for this. Likewise, I don't have any problem with a business owner who, for religious reasons, questions homosexuality.
I don't think it's "discrimination" to say that being gay is a choice, or to generally have negative opinions about the behavior.
That said, I would never patronize a business that had a "no gays" sign out front, or that refused to serve gays in any capacity simply out of spite. I would never patronize a business that used hateful gay slurs, or that depicted gays in an offensive way, or that I felt encouraged or incited hatred against homosexuals.