You needn’t Google far for recent case studies of Internet outrage. Log in to a social network and you’ll find it directed at celebrities and civilians alike. (See: Woody Allen, Stephen Colbert and Justine Sacco, the former communications director for IAC who posted an insensitive Twitter message about AIDS in Africa.) Politicians are a perennial favorite: Chris Christie, Rob Ford, Anthony Weiner. Then there’s the bigger game: courts of law, social movements, news media outlets, corporations and governments that have rubbed people the wrong way.

As a now-hackneyed joke goes on Twitter, “What are we angry about today?”

Bile has been a part of the Internet as long as Al Gore has; peruse any epithet-laced comments section or, worse, a chat room. But the last few years have seen it crawl from under the shadowy bridges patrolled by anonymous trolls and emerge into the sunshine of social media, where people proudly trumpet their ethical outrage.

A 2013 study, from Beihang University in Beijing, of Weibo, a Twitter-like site, found that anger is the emotion that spreads the most easily over social media. Joy came in a distant second. The main difference, said Ryan Martin, a psychology professor at the University of Wisconsin, Green Bay, who studies anger, is that although we tend to share the happiness only of people we are close to, we are willing to join in the rage of strangers. As the study suggests, outrage is lavishly rewarded on social media, whether through supportive comments, retweets or Facebook likes. People prone to Internet outrage are looking for validation, Professor Martin said. “They want to hear that others share it,” he said, “because they feel they’re vindicated and a little less lonely and isolated in their belief.”

Certainly, outrage can function as a corrective or anguished expression of helplessness, punishing the offending party if he, she or it has not been given any official penalty; think of George Zimmerman. Moreover, it can double as effective activism, forcing a response from the powers that be, as in the case of Ms. Sacco, whom IAC fired the day after her post went viral and who inspired someone to create a website with her name that redirects visitors to the nonprofit alliance Aid for Africa.