Why do conservative talk show hosts call people they disagree with "stupid" and worse?

I’m sure this has been discussed before, but I cannot bring myself to understand why commentators like Glenn Beck can’t rigorously disagree with others about even the most important issues without resorting to ugly slurs. In many, maybe most cases, the people who call others stupid, dangerous, anti-American, etc. have never met their targets, let alone know the full context of their views, beliefs and sincereity. Sure, I know this kind of aggressive commentary is supposed to be part entertainment, but speaking for myself, I am not entertained, just disgusted and afraid about the often mindless loyality of their viewers. Thoughts?