Political correctness isn't stifling any debate. In fact its influence is extremely over-rated by a lot of people. A lot of this idea is rooted in misconception on both sides, in my view.
Nobody is stopping you arguing/debating by calling you un-PC. They're being irritating, sure, but they're not stopping you from arguing a point of view. Try arguing it afterwards, you'll find you can still do it without any fear of persecution. You're just being argued against on grounds that you find annoying or invalid.
Political Correctness is fine when it's genuinely working against abuse. For instance, yestarday I was participating in a school workshop, and one of the kids made a hateful comment (which I shan't repeat) regarding the ethnicity and sexual orientation of one of my colleagues. It's pretty clear that wanton hate isn't acceptable, and 'political correctness' has a place here.
What does irritate me is when Political correctness is taken to an extreme extent. For instance, the other day I used the phrase 'Don't be such a big girl's blouse' and was challenged by someone for unknowingly endorsing gender stereotypes. This is where 'political correctness' starts to get annoying and is then accused (with not much real basis) of stifling debate and expression.
If I wanted to keep saying the phrase, there was nothing stopping me. I was just being challenged in a way I found very irritating.