"Troll" implies malign motives. Someone can be a massive dick with complete sincerity.
But we don't actually care about motivation, we care about stupidity.
Personally I suspect leaving the comments of the poster in question visible, buried in a slag heap at -12, is just fine. You have to want to look, and examples of blithering stupidity are often useful as teachable examples.
Actually, I think it would work if the tag that indicates number of replies to a downvoted-to-oblivion post also had the average karma for the thread. This would give a fast way to judge whether the thread would be worth reading.
A brief line from this comment indicates that the author of the cryonics-critical comment quoted here was perhaps not the one that deleted it.
Was it deleted by a moderator?
Honestly, the decisive downvoting seemed to do the trick of hiding it from casual readers who don't want to see the long annoying rants. I don't think it was casting any doubt on the credibility of cryonics.
While it sounds like the author regrets posting it, I would think they should be allowed to delete it themselves.
Edit: Originally titled "Cryonics critical comment deleted?"