I'm not sure this is necessarily an unavoidable fate for internet sites, even communities. You can keep the signal to noise ratio decent if you've got an activ

I'm not sure this is necessarily an unavoidable fate for internet sites, even communities. You can keep the signal to noise ratio decent if you've got an active team of moderators, fairly heavy pruning of content that doesn't add anything to the conversation and the willingness to say no, my site doesn't offer 'freedom of speech'. Unfortunately, most big sites seem to be built on the 'leave it as a complete free for all with no moderation whatsoever' model, which immediately stops working the minute the memberbase expands from early adopters to every Tom, Dick and Harry. That's why Reddit, Twitter, etc have had so many problems. They were built with the idea of 'anyone can say virtually anything' in mind, then realised it would lead to massive amounts of trolling and personal attacks and questionable content, then dug themselves an even deeper hole by trying to moderate the site in woefully biased ways.