Special reports interrupt regular television programming. The event is treated as a national catastrophe. For weeks afterwards TV news pundits ponder his actions. Given the horrible nature of this act it is hard to answer honestly. If we are able to leave good and evil aside we are forced to admit that this act of violence was most affecting.
People are numb to art.
One can put anything on a canvas and no one will bat an eye. You can say or do anything in music and no one is shocked. None of it is taken seriously enough to be considered as a sincere statement. But by employing extreme violence the artist was able to capture the focus of the national media and cut through the public malaise to make them seriously consider the meaning of this act. Whether we like it or not the artist achieved what few artists ever are able.