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.
You know what - I am rather glad my comment was deleted on less wrong - good reason for people not to post on there.
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?"
This still doesn't answer the question: why isn't down voting good enough? I'd rather rely mostly on community moderation rather than a few specialized moderators.
As a side note, perhaps users with sufficiently negative karma should have their comments hidden by default?
The main issue isn't that downvoting isn't good enough but that we don't want to terribly damage the signal to noise ratio. Thus, we don't want massive amounts of spam or trolling in threads, even if it has been downvoted. But this argument is fairly weak. If users could be banned without having comments deleted that would solve the primary problem.