Actually I think most political parties act kinda cult-like.

Conservatives see Liberals as:
Gun-hating, tax-raising, America-hating, UN-loving, handout-giving, anti-Christian, hypocrtitical hippies who are all closet-socialists and likely on some sort of illegal substance.

Liberals see Conservatives as:
Gun-loving, poor-hating, closet-racist, America-loving, UN-hating, Christian-Fanatic proto-fascists who have never had a day of fun.

It's just a way to label people so that you don't have to listen to them anymore. If I'm a "liberal", that's all a conservative will ever need to know about me. That makes anything I say in the political realm heresy to the conservatives, and therefore they shouldn't listen to the ideas other than to find some way to shut me down. If I'm a "conservative", that's all a liberal needs to know. They already know that I'm a sad ignorant conservative to be shunned. Think of it as a way to keep the faithful from going astray. It's the same thing with religion. If I'm not the same religion that you are, than anything I might say about religion is automatically suspect, because I don't know "the Truth (TM)". That way a Christian won't listen to what a Muslim says about God, and therefore think of other possibilities. Nor will a Muslim wonder about the things a Christian says about God. All of it is designed to keep people from listening to the other side and thus possibly questioning the orthodox viewpoint. Very human. It happens everywhere.