It is certainly not retarded and it may be a simplified generalization but not overly so. This forum is not one where citing laws and regulations would make much sense. And only a pedant would say something like ‘well they have to follow the law.’ That goes without saying. The question is whether in general it would be illegal for a business to require customers to wear a mask. And the answer is no. Are there exceptions? There may be, as you allude to above. But they are few.