Yes it is. And while you are walking around outside you have the right to wear that bag. But I can keep you from my home. I can keep you from entering my store. I can keep you from entering my bank. The same laws which allow the government to control the items one can carry into the airport and onto the planes can also control what people wear in those locations, and elsewhere. The same laws that can prohibit you from entering a bank with a loaded crossbow can prevent you from hiding your identity. Liberty does not endow anyone with the freedom to do whatever they damned well please. That would be anarchy. Limits must be in place to ensure public safety.