"gotcha...no, I got you...gotcha...no, I got you...gotcha...no, I got you...YAWN...BIG SIGH."
Online debates can be informative, challenging and stimulating, but rarely do they lead to a meeting of the minds. In person, there is usually peer pressure if not internalized pressure to meet others half way, to acknowledge they are right about some things, to show your manners, your generosity, your willingness to listen.
Online discussions have opposite pressures -- to score another point for your side with a brilliant insight or sharp quip, to one-up, to have the last word. These discussions end not when people agree, or even when they agree to disagree, but when they simply run out of steam (energy) or participants get bored by the repetitive circular arguments.
I saw a cartoon in which wife asks husband why he is staying up so late. "I have to finish this debate," he says. "Someone on the Internet is WRONG." To persuade all the people on the Internet of the errors of their ways is quite an undertaking!