How about this.
Name things that would not be possible by withholding guns from the public.
Pick a country. But if you pick like Soviet Union, where gun ownership was very restrictive and hand guns were very limited. Getting shot a by a gun was very rare.
When then Soviet Union fell, the crime went up.
It's pretty proven that gun control works with an adequate police/military force. Someone already pointed out Singapore that one of the lowest violent crimes in the world.