Every few years, the American public is stricken with a full-blown moral panic, and we’re in the midst of one now over Todd Phillips’ “Joker.” The paranoia that the movie will drive a lurking army of incels and troubled young men to fits of violence is not just pure fantasy. It also reflects a refusal to look at the real problems of our society — including untreated mental illness, endemic poverty and drug addiction.

This isn’t the first moral panic in America. In the 1950s, comic books were widely seen as dangerous to young minds, and psychiatrist Dr. Fredric Wertham argued that comic books would drive children to lives of addiction and delinquency. The public was so captivated by Wertham’s subsequently debunked proclamations that the Comics Code Authority was created to censor comic books and enforce moral standards. It remained in operation until 2011.

At various times, Dungeons & Dragons,...