(Also to Richard Corbeil):  If you go into business as a bakery, and someone comes in and wants a cake, that's not forcing you to do anything you didn't set out to do.  If the person is rude, verbally or physically abusive, hasn't paid in the past, or is obnoxious in some other way to the point of being a public nuisance or hazard---You should be able to refuse service to that person, regardless of race, religion, sex, or sexual orientation.

It's when you make the decision that you shouldn't have to serve a type of person based of prejudice of that type that you get into ethical trouble---Say, if you don't like christians because they're pushy and try to get tenets of their faith passed off as law.  Sooner or later the christians who want your services are going to have legal recourse to come back and say, You can't refuse service to me because I'm christian---You have to make my wedding cake.  You can still refuse---But then there are legal penalties.  So much for semantics.