Most people - including most people in this thread - are against political correctness because they either: a) misunderstand what it really is, or b) are prejudiced and don't like being called up on it.
When people hear "political correctness", they think of this straw man set of laws that say you can't even mention a person's race or sexual orientation without being called a racist/homophobe, and yet at the same time you have to give preferential treatment to any minority or female. There are very few people who actually promote that kind of PC, and yet the anti-PC crowd acts as though they're everywhere. The reality of political correctness (like the reality of feminism) is that it only asks for people to not discriminate
against minorities and oppressed groups. If three people apply for a job and one of them is a Muslim woman, you don't have to give the job to the Muslim; but if the Muslim woman is clearly more qualified but you give the job to a white dude just because you dislike Islam,
then you're politically incorrect.
In other words, political correctness = not being a dick.
Which brings us to the second type of anti-PC person: the stupid bigot [http://vice.typepad.com/vice_magazine/2009/07/london-babes-of-the-bnp.html]. These are the people who say things like "I'm not racist, but I hate it how I can't call someone a ****** without being called politically incorrect.
They say it all the time!" It should be clear why this is a nasty kind of thing to say.
EDIT: This sort of thing is totally ok in my definition of political correctness:
Dahemo said:
I used to work in game retail, and a customer asked me where a certain item was, I told her it was just in front of "the young black lady" across the room. The customer I was talking to looked at me quite worriedly, then walked over. I felt like I had said something wrong, but patently it's just PC sensitivity.