We have our fair share of whackjobs, but they don't have guns either, so why couldn't we defend ourselves? At least if we tried to defend ourselves and lost we'd probably get beaten to a bloody pulp, but live.
I can also run from whackjobs, I can't run from bullets. I can assist, or receive assistance from others before the whackjobs cause too much harm, with guns they can kill you or someone else before you even know they're there.
Knifes and other concealed weapons are illegal too, so most of the "dangerous type" (criminals, gang members, whatever) rarely bother carrying them cause it's an excuse for the police to throw you in jail.
As for the Police, I don't know what they're like in America but they're a pretty decent bunch people here. Sure, you get your few bad apples, like in every job, some that may lay a few unnecessary wallops with the baton, but never shoot anyone. They're not superior, they're doing a job, but that job comes with it's own set of values and laws which they must follow.
