I don't know what libs can say now in lieu of the idiot restaurant owner in Virginia throwing out Sarah Sanders. They obviously agree that a business owner should be able to refuse service to some customers for certain reasons having nothing to do with the comportment of the customer at the place of business. They just don't realize it yet.
The argument is (playing devil's advocate) that political beliefs are not a protected class, while religion, race, gender, and sexual orientation are.
In other words, one can discriminate against someone for political beliefs, but not because they are black, gay, or Jewish.
A Jewish shop owner can kick out a Stormfronter from his restaurant. A Stormfronter however, can't have a 'no blacks allowed' sign.