Or even "If you supported [insert some popular gay-rights political thing here], you are not welcome here", to make it about politics and not the sexual orientation of the potential customer.
The Left would go nuts.
Remember the Chik-Fil-A outrage that came when libs found out they supported traditional marriage. They did not refuse to serve anyone, but Boston and Chicago mayors wanted CFA barred from their cities.
These are not good people. They are going to try and turn up the heat on all of us. We better be aware and fight back.