Pure fantasy? I don't think so.
If you know anything about muggers, you know they are bullies, and what are bullies? They are cowards. They rely on fear and intimidation. Once you stand up to them they end up becoming push overs even when they have the victim outnumbered and outgunned.
If my weapon was concealed, you wouldn't know I had a gun, now would you. So, no, you'd be in danger because you'd be caught off guard.
Most criminals don't want to have a shoot out. They'd rather get what they want, push around defenseless people, because it's easier. They don't want conflict. So when they come up against conflict, they panic. Guess what corrupt governments want? Gun control. Because it's easier to run over someone with your military than it is to fight against a population that is armed to the teeth. I mean it's common sense. Why would a criminal risk his life to take down someone they know is armed. They usually won't even fight back once they see an innocent with a gun, unless they have an army of gang members backing them up. But even then, they just end up being push overs.
Here is an example of guns saving the day.