The purpose of civility and politeness is to make people comfortable and at ease. Part of civility is to not refer to people by names they (and, lets face it, you too!) find offensive. It has nothing to do with your political agenda, it is downright civilized behaviour. Any discourse, personal or public, that uses slander or offensive, diminutive and contemptuous phrases intentionally and repetatively is inciteful and non-democratic. One of the basic principles of democracy as I see it, is the ability to respect even your opponents.

Political Correctness is a way to avoid showing such disrespect even to your adversary.