it's the snide way in which they attempt to push across their particular view/opinion as right and that you must be out of your mind to think any other possible way.
And even worse is the sheep who follow it. For example, I saw James Taylor once in Huntsville, AL. You know it's a pro-Republican crowd. Well he starts off on his anti-Bush tirade, and the audience, stunned at first, then laughed and applauded the guys political views.