Ok, so we have established that blacks kill each other in far higher numbers than any other race. Not racist just fact. Why is this? Is it because their brains cannot process the idea of consequences in the same way as other races? What is causing all these senseless murders? Poverty? Under developed frontal cortexes? Societal pressures?
I believe primarily the one you listed regarding intellect with the other factors exacerbating this most important factor.
Despite the vile entertainment media featuring black characters as wizards, heroes, and protagonists cracking cases, movies like Boys in the Hood, Juice, New Jack City, Colors, and Menace to Society, portrayed blacks at their worst and instead of somehow showing that being violent, criminal, degenerate, slovenly, and illiterate is not the right way to be, it simply reinforced such. If I remember correctly, there was even gang violence at movie theaters showing Colors.
I remember being in eighth grade in 1993 and the day after the video for the song, "Throw Ya Guns in the Air", middle-class wiggers and students of other stripes were singing that degenerate song which glorified violence, with the video embellishing such glorification.
In some cases such a video would do the opposite of what the media intends to do (have the races co-mingle) and would have some people thinking, "I'm staying the hell away from such people", which is what sane people would think after watching physically jerky and confrontational gangs of people screaming for their penchant for robbery, assault, and murder.