Unfortunately, for every good citizen black person who speaks well, shows manners and consideration for others, there are thirty examples of the exact opposite. Think about all those mobs of black teens creating trouble in malls or at restaurants. Other races do it too, absolutely, but we blacks seems to have a corner market on self expression via destructive behavior. It doesn’t help having a president who blames all but the perpetrator for towns going up in smoke.
As you say, it's not all of them. But it's enough of them.