I think it exemplifies a broader behavioral pattern. The counter-cultural left of the 1960s attracted assorted self-centered megalomaniac because it gave them an excellent chance of becoming instant celebrities by a rather primitive means of flashing a finger at authority symbols, which included hurling insults and obscenties, silly contumacy, denoucing generally accepted views while embracing extreme positions, etc. Hyperbole is an excellent self-promotion device because it is easy to employ but has a drawback that it can be interpreted as a sign of lunacy rather than celebrity. The context of counter-cultural movement reduces that danger by creating an interpretative framework that redefines crackpots as celebrities.
Today, crackpot behavior is no longer the hallmark of counterculture, let alone progressivism. In fact, it is pretty main stream (hip hop) and right wing (Rush Limbaugh) - so maintainig an intellectual celebrity status throuigh these means is rather difficult, if at all possible. Therefore, a cleberity status craving megalomaniac must resort to different yet essentially similar artifice to maintain his celebrity status - again by flashing a finger, but this time at his countercultural audience, by becoming ultra-orthodox. This way they again stand out of the mainstream obscenity hurling crowd.
Hitch and Horowitz are perhaps the most prominent but not the only cases.
This should NOT be construed as an argument that all "traditional" counter-cultural lefties were crackpots and megalomaniacs seeking celebrity status. It means that most, if not all, social movements and revolutions often serve as vehicles for such opportunistic individuals, who may be the minority but give these movements and revolutions a bad name.
Wojtek