Wait. "waterboarding isn't torture" is not a question on which changing one's belief is evidence of rationalism. Asking or answering the question at all is a political ploy only. The rationalist reaction is to taboo the word "torture" and reduce the question to something physical and testable.

Tabooing a word isn't the only response that's rational, especially because that is a not even well-known technique. In this circumstance, what Hitchens change of mind essentially meant is that he agreed afterwords that the experience was so unpleasant that any definition of "torture" that captured his intuition of the term would have to include waterboarding. Cyphergoth's point stands: Hitchens was willing to change his mind when confronted with evidence. Whether there might be a marginally more rationalist thing to do is somewhat besides the point.