Lets define un-politically-correct language first.
First, the "N" word. Basically it carries with it the connotation of "I'm already better than you, so don't start no $#^! with me, Boah!"
And where does the utterer of the pejorative 'she-male' stand in relation to the pre-op transsexual have-to-work-in-the-sex-trade person he (almost always the speaker of this term is a 'he') is referring to?
Currently, if you use the terms "African-American" or 'Transgender' instead, there is not that automatic offset that connotes the speaker is on some sort of moral or power high ground looking down on the person referred to.
Sometimes it's nice to call a spade a n*****, but it's almost never polite and almost always demeaning.
PC terms also tend to be on a treadmill -- a new term without the emotional baggage of the previous term picks up that emotional coloring that signals an offset in status, and bye-the-bye is replaced by a new term. Witness colored -> negro -> afro-american -> black -> african-american ->

The same thing happend in the hispanic community, along with fragmentation where different communities took on one term as being 'correct', while other communities saw the same term as disrespectful.
That is also why - while it's scientifically incorrect - I prefer to refer to myself as 'transgender', even though it is seen as an umbrella term including weekend warriors (a slightly pejorative term used here for example,) and anybody else that doesn't fit the binary. A segment of our poplation gets ung-up on the emotionally-loaded term -sexual that is in 'transsexual', and can't get past that to see me as anything higher than pond-scum. But if I can get them to see me as 'transgendered', I get an instant promotion -- maybe not to status of 'equal', but far better than pond-scum.
Sorry, I see a need for 'politically correct' speech, if only to remove rhetorical advantage from bigots and those who are prejudiced. Chapter 7 of Steven Pinker's book, The Stuff of Thought, has a great analysis of how certain terms trigger knee-jerk emotions in people, and makes the case for politically correct speech to defuse those emotions in susceptible individuals.
Just my thoughts;
Karen