The only thing that can stop bad kids with guns, are good kids woth guns
But are good kids going to walk around in gangs with guns pretending to be the world's police and not become that bad kids?
in your world only the police (government) and criminals would have guns. Would you feel safe? Part of the reason for the 2nd amendment is so that citizens can protect themselves from the government. They saw the results of over-powerful governments in Europe, that's why they put the 2nd in the constitution.
A little American history might do wonders for your understanding of this country.