It seems to me that this is just a response to the laws of nature. I'll expound a bit.
Nature abhors a vacuum. Does not matter what kind it is; the natural forces of physics, fluid dynamics, human action, etc all try to fill in what is void.
In terms of self-defense, it comes down to the "haves" and "have nots".
I have a morals and ethics, therefore I have things of value (family and possessions), which I protect with rational levels of defense (locked doors, safe storage, and firearms). Someone attacks my domain or family, I'm going into full defense mode. Someone may die; probably not going to be me. Unfortunately, I'll have to defend my actions despite a criminal's intent. And in his place, another criminal will step in; his void is filled.
I'd be willing to move from the USA to another country, IF I thought there were any "better" place to live. If ALL morons, criminals and general miscreants could be heaped into the center of this land-mass, I'd move way north or way south. If we could rid Canada or Mexico of all problem folks, they would be great places to live. Or we could rid the USA of undesirables, and toss them elsewhere.
But alas, creating a void only causes nature to want to fill it. You cannot escape stupidity; stupidity (and its cousins of greed, malice, sloth, wickedness, etc) follows sanity everywhere it resides and tries to muck up an otherwise perfectly decent life.
Just my .02 here.