Completely agree. Associating my actual views with my real identity makes me uncomfortable as well - not so much concerned about what Facebook would do with that data, more concerned with the fact that it will cause people I know or have a strong chance of meeting to dislike/hate me for a reason that I'd rather not give them.
Also, having a "debate" over FB sounds only moderately more pleasant than having a debate in the comments of a Youtube video.
I don't do it because it's pleasant. In fact, it's often really stressful. I do it because I think it's crucial, in the same sense that I think any sort of political or social engagement is crucial.
As far as the risk of people hating me, I try really hard to always be respectful of people I debate with. I think for that reason, I've been able to keep friendships with people I regularly have some pretty intense disagreements with.
Also, having a "debate" over FB sounds only moderately more pleasant than having a debate in the comments of a Youtube video.