Can a business be sued for discrimination if they refuse to serve a customer for an opinion?

Say, for the sake of argument, everyone in the bar was a straight, white, man, who was 5'8, and they were all from the same state, same city even, to really eliminate any chance that this was based on race, sex, or sexual orientation. And then say that one person said "I think that (insert tax here) should be raised from 20% to 25%". Instantly the bartender turns to them and says "Sorry I can't serve someone with that opinion anymore", assume they call over the manager or the owner, who is also a straight white 5'8 male, and they say the same thing and ask them to leave otherwise they are trespassing.

Can they be sued in anyway? This is not based on real events in any way, I'm just wondering.