There is no law that says people can't think marriage is between a man and a woman. There is no law that says little boys shouldn't wear pink or little girls shouldn't wear boxer shorts. But we were all raised with these things being what we're used to. If people think marriage is between two people of the opposite sex, that is their right. You're now trying to regulate the beliefs of private citizens. That's scary.
Freedom of speech is not freedom from criticism.
Now suppose that one would support traditional marriage, and also support SS Civil Unions? What then? Also a bigoted position according to your definition?