How many blacks living in America are descended from slaves, and how many are recent immigrants from the Carribbean and Africa?

Who form the bedrock of the black middle class? Who are responsible for pressing their case in Brown v. Board of Education of Topeka? Who were the lights of the Harlem Renaissance? Who founded Howard University? Who initiated and drove the Civil Rights movement of the 1960s with so much courage and principle? People recently arrived from Africa and the Carribbean? I don't think so!

This is not an American black cultural problem; American blacks have just as much couth as everyone else, as well as a distinct and admirable cultural heritage in America.

There is a portion of the black population, however, and also a portion of the white population, that falls short in its responsibility to impart civilization to their young people. Part of this is the function of poverty, and of not knowing how. Part of it is self-absorption on the part of the adults, and low expectation on the part of the rest of society.

Why are the atrocious children I encounter not part of a white cultural problem, but atrocious black kids encountered by others are considered part of a systemic problem with black culture?

Put the responsibility where it belongs. It's not a black thing.