If you refused their business because they were jerks or because they wore red shirts- perfectly legal.
So, refusing service because you don't like someone's shirt is morally acceptable? Then why in the fuck is it so objectionable to refuse service that would conflict with your religious beliefs?
Refusing service because someone is an asshole or because of the color of their shirt is both legally and morally acceptable.
Refusing service because someone is black or Jewish or gay or Japanese is not legally acceptable in several states, and not morally acceptable in any.