Megan McArdle is usually pretty incisive. I like this summary from Twitter's Harassment Problem Is Just Business.
We shouldn’t have to face a trade-off between having a decent online community and having Twitter be an economic success. But life is full of trade-offs. Online communities have been struggling to solve the problem of abusive behavior for decades, and no one has come up with anything that consistently allows a system to be a) open to the public, b) anonymous, or at least pseudonymous, and c) civil. These three desirable features seem to be impossible to assemble in one package. Which is why so many websites have shut down their comments sections.Access, anonymity, civility - pick two.