Maybe it's just my personal experiences, but I interact with plenty of black people on any given day. I'm not going to claim "some of my best friends are black," but I live in a city where blacks are a (shrinking)majority. There is certainly a black underclass, but the criminals in that group are much more likely to prey on other black people.
This idea that the criminal element of the underclass is actually going to organize (like in that movie The Warriors) and take over the city is fiction. We're talking about criminals who have a tough time getting out of bed before noon and whose highest aspiration in life is getting a pair of shiny new sneakers, a 40-ounce of malt liquor and porn. People like that are never going to get their crap together enough to be anything other than a nuisance to regular society.
ROTFLOL!
Our experiences are probably pretty similar. I still remember in college I had to take Intro. to Sociology. The one thing I remember from that class was a study done in the 1800's found that prison inmates were dumber than the general population. It struck me how obvious that is. You have to be pretty stupid to keep walking down a path where the vast majority end up dead or in prison.