It is the difficulty that is the problem, I think.

Imagine a customers comes in and, somewhat aggressively, refuses to wear a mask and says it is their choice, and the government agrees, and what are you going to do about it?

Yes, you can refuse. When you do so, you are probably refusing their custom for all time, and possibly that of some of their friends. That is not an easy decision after a year or more of very little income.