Why Do People Ignore Or Deny The Existence Of Decent Black People?

Why is it that when the few black people that some people know are those rude, uneducated inner-city ghetto folk on welfare, they insist that every black is like that? There are some good and educated black people out there, but some of you people always just disregard them just because there are bad ghetto thugs! Why insist that blacks that can do anything nice and useful are like Santa Claus and the Tooth Fairy? What about black people like astronomer Neil deGrasse Tyson? Why not make fun of the English instead?