Did you hear about this? Some anti-war nutcase undergrad tracked down College Republicans from his school through Facebook. He showed up at one lucky guy's house acting like a military recruiter, but ended up in fisticuffs with the guy and his roommates. To top it off, he waited for the police to arrive and argue his case. The Rhodes scholar is out on bail at the moment, but yeesh.
I went to college with people like this. Absolutely no inhibitions, and the overwhelming self-assurance that everything they do is right, especially in pursuit of The Cause (whatever "The Cause" happens to be for that person).
I guess this just reinforces two things for me: That you should mainly discuss politics with friends who won't wig out on you if you disagree with them, and that you should always be very careful about what you put on Facebook.