As far as I know people are allowed to wear masks in public. They are not always doing it for bad reasons like the punk in the video was. People wear masks for Halloween, or to protect themselves from inhaling dust, or to protect against disease if they have a cold. A person at a protest might want to dress up in a costume to make some point or other.
Writing a law against wearing a mask which does not have unintended consequences may be a bit trickier than one might think.