relevant in science writing, where opinion matters less and facts matter more. Misreporting by journalists is part of the reason that people believe that MMR is dangerous , or that homoeopathy is effective , or that evolution is only a theory . Even one or two well-informed, articulate comments underneath that sort of silliness can destroy the unearned credibility of a factually incorrect piece. Also, we can actually learn things. It's a shame that for every carefully researched comment with bullet points and a PubMed reference, there are a dozen saying "Did you actually get paid for this so-called 'journalism'?", but that's how it goes, and it does mean that I can't trot out any old nonsense without getting called up on it. Most of all, though, it's fun. A column or a story or a blog post with comments switched off is inert, boring, a dead planet. It just sits there. People look at it, and they move on. Nothing happens. An active comment thread is vibrant, full of life. Yes, some of that life is ugly and smelly and vicious. But it's life, at least, and it's normally preferable to tomblike silence. But I want to clear up one thing. When we remove your comments, it is not a free speech issue. I know some of you think it is. "This used to be a free country" is a familiar refrain, usually underneath a comment that has been deleted or edited by moderators. Censorship, free speech, the thought