I respectfully disagree. I think you underestimate the power of video, and the power of a 24/7 global media culture to disseminate such broadcasts in a way that ensures that we are never free of them again. In this age of file sharing and homemade filmmaking, clips of Cho are no doubt already being edited into loops for the productions of other malcontents whose names we do not yet know. Yes, Cho would have gotten publicity without the video, but it wouldn’t have been on his terms; his elaborate broadcast allows him to dictate those terms to significant degree.
From the parts of the video I saw (yes, I watched it, too), Cho’s rants are breathtakingly narcissistic, self pitying, and grandiose – right out of Psych 101 under the God complex, complete with references to Christ. Cho’s broadcast may not be the impetus for others to commit mass murder who otherwise would not have, but it does offer them a significant solace in debating whether to go through with it: a promise of a kind of eternal life in the media age, a promise that they will at last be listened to. That seems like too much positive reinforcement to me.
p.s. I don’t think you would be hypocritical to watch the video while also criticizing NBC for airing it. You and I do not control their broadcasting decisions, but we do have to live with them.