There’s a cartoon that has become something of a meme since it was first published in 2008 in the American webcomic xkcd. In it, a stick figure sits hunched over a desktop computer, typing furiously. A voice off-panel asks, “Are you coming to bed?”

“I can’t,” the stick figure replies. “This is important… someone is wrong on the internet.”

What exactly fuels our compulsive need to comment? Current events, local gossip, pop culture moments—it doesn’t matter. Open up Twitter and you’ll find a dense thicket of other people’s opinions. Sometimes, this constant stream can be frightening. Other times, it can be fun, smart, even life-affirming—say, the outpouring of love one witnesses during a global sporting event. Or, equally fun: the outpouring of snark when a pub...