Besides the points already made addressing your Hell's Angels scenario, most people would still frequent the gun free bars. You don't go to a bar primarily because they allow you to have guns. You go because you are meeting friends, a date for drinks, to dance, the ambiance of a certain bar, to see a band, whatever. You will still do this with the gun in your car and only a real stick in the mud child wouldn't want to enjoy these things because they can't have a gun on their hip. This is the minority.
So the bar owner, whose primary cares are cash inflow and as few hassles as possible, will do fine to ban them from his bar, if it's a bar that people would want to go to anyway.