Yes it is. I don't agree with discrimination, against any group. But making poor business decisions should be legal, that's not the government's business.
Yes,the government shouldn't be the one determining such things in a private business.
Yet to have a business that has signs up saying,"no blacks,no women,etc"is blatantly anti-American and only serves as a propaganda tool for radical Islamists and others who would use businesses with these policies to defame America as a whole.