When you teach a group of people that it's OK to verbally abuse and attack *anyone* who thinks different than yourself, it's only natural that they will turn that intolerance to internal differences within the group to make it ideologically pure.
You even see this behavior in churches, I've had my church split because of the pastor's interpretation of a verse by those who insisted that the Bible cannot be interpreted but must be accepted word for word. A group of people who gathered together in the name of love, broken apart over what in the long run, was a minor issue attempting to be "pure".
Of course the GOP is just as guilty in many cases, case in point, look at the primary battle this year. Unfortunately, intolerance, ironically presented as "tolerance", is a genie that is hard to put back in the lamp once it's be unbound.
If we are lucky, the Dems and the GOP will both self destruct through this process and split, creating two new moderate parties. That will give us a 4 party system that might have a chance of actually working.
But I doubt it.
