I think there would be immensely less crime.
I think one of the big causes for our gun violence is that in cities you find tons of people who have either no experience with guns or a complete aversion to guns. So really they are just unbelievably easy prey for a would be criminal. It's hard to imagine you could rob a store with more than one person in there if everyone has a gun.
Criminal points gun a cashier
but everyone has gun
6 customers immediately shoot criminal and cashier is already starting to draw as it happens
Or at least that's how it goes down in the spaghetti western in my head. It wouldn't end good for the bad boy is the point