About 18 months ago I stopped posting regularly on HN after my former account was downvoted into a type of purgatory that was impossible to escape from. I still read the interesting articles and the occasional interesting discussion, but something I discovered in the intervening period of participating in unmoderated/uncensored forums is that trolls make you THINK. There are some exceptional trolls out there on the interwebs, some of whom do it as a day job. They post articulate but specious arguments that are very difficult to debunk unless you do meticulous research, double check your calculations, edit your reply for succinctness, remove any possible semantic ambiguity. I think there is an argument to be made for the stimulating effect of trolls on the rigour and effort of the opposing participants. I agree however that trolls can and have destroyed valuable forums of discussion, but so has lack of interest.