Evolution makes quick-changing 'control knobs' because it takes way too long to adapt from just random mutations.

One of these clearly is MAO-A that controls how much of certain neurotransmitters you have. Blacks have the most-violent variation at ~5%, whites ~0.1% and Asians at basically zero. Its correlation to violence/impulsiveness has held up over and over in studies. The various animal studies where they breed behaviors in a few generations also proves there are these 'control knobs'.

Uncivilized behavior could be bred out in just one or two generations, so for it to still be around is because it's being rewarded. Our Western societies are soft and easily taken advantage of, so the blacks' control knob has settled on a level that's sustainable - the violent 'control knob' setting can easily reproduce by rape and promiscuity, but is tampered down by prison and being murdered young.

Ironically we'd have to be uncivilized to civilize those people.

tl;dr it's our tolerance for black behavior that makes them stay people that we have to tolerate.