The problem is downvoting fatigue when someone posts multiple troll comments. I support banhammering all of a user's posts when they're all being downvoted and are all clearly not suited to LW.
Another fix would be to have comments by users with sufficiently negative karma hidden by default.
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?"