As Mr. Dorsey told Wired in April, “A more open exchange of information is our purpose, and it’s a noble one.”

The social-media overlords seem sincere when they describe their high-minded intentions. They talk much less, however, about the money they make from their users’ relinquishment of privacy.

The willingness of those who make daily use of Google and social media sites to offer up their likes and dislikes, not to mention the details of their spending habits and internet wanderings, provides Mr. Zuckerberg and his fellows with the personal data that is the holy grail of modern advertising. It also gives them an endless stream of free content to put those ads beside. Their users’ endless posts, spats and vacation pics make for the ultimate reality show.

At times, social-media feeds are about as authentic as a standard reality show, too. Witness last week’s story about the former Fox News anchor Jane Skinner Goodell, who is married to Roger Goodell, the commissioner of the National Football League. Turns out she was using Twitter to attack journalists whose work was critical of her husband, but, as The Wall Street Journal reported, she was doing so through a fake persona with a laughably unimaginative pseudonym, “Jones smith.”

Ms. Goodell’s use of an online disguise suggests how hard it is to be yourself on social media, and the recent experience of the ESPN host Jemele Hill shows even more clearly the perils of mixing private and public personae on Twitter.

ESPN and its parent company, Disney, initially gave Ms. Hill a pass for violating their social media guidelines when she used Twitter to call Mr. Trump a “white supremacist” after his equivocation over the deadly rally in Charlottesville. The Disney chief Robert A. Iger said he respected her urge to speak out as a black American.

Then she used Twitter to call for a boycott of the Dallas Cowboys’ advertisers after the team’s owner, Jerry Jones, said he would bench players who kneel in protest during the national anthem. ESPN noted this had been Ms. Hill’s second violation. But let’s face it, this time she was going after ESPN’s bread and butter.