But such a large audience’s benevolence — turbocharged by the tendencies of social media — stretches only so far before it curdles into something far more sinister: its own sort of conservatorship, with constraints dictated not by a judge, but by the whims of an online mob.

But this time, it isn’t just the paparazzi following Ms. Spears’s every move; social media is the new tabloid, where anyone can play the role of gossipmonger.