Beck's whole schtick is to trade on vague fears that find their roots in the worst things about us. Racism, suspicion of others who aren't like us, being old and stodgy, uneducated, reactionary. He is a con artist, weaving into his political message a narrative that simulataneously warns his already uncomfortable listeners that the black man is about to take over and exact justice but that if they will only do things like buy from his sponsors and vote for the candidates he endorses, then white suburbia shall reign once again.
Olbermann is just wicked smart. He antagonizes people like Beck, and those who follow him, because he shows them to be the freaks that they are.