To be sure, some conspiracy theories turn out to be true.
US Republican officials, operating at the behest of the White House, did, in fact, bug the Democratic National Committee’s headquarters at the Watergate complex.
Beginning in the 1950s, the US Central Intelligence Agency did, in fact, administer LSD and related drugs to unknowing subjects in an effort to investigate the possibility of “mind control.”
In 1947, space aliens did, in fact, land in Roswell, New Mexico, and the government covered it all up. (Well, maybe not.)
Even when false, most conspiracy theories are harmless. Consider the theory, popular among younger members of our society, that a secret group of elves, working in a remote location under the leadership of a mysterious “Santa Claus,” make and distribute presents on Christmas Eve.
And in a free society, conspiracy theories must be allowed even if they are both false and harmful. However, sometimes conspiracy theories create real dangers.
If people think that scientists have conspired to cover up the harms of vaccines, they will be less likely to vaccinate their children. That is a problem.
Unfortunately, beliefs in false conspiracy theories are also peculiarly resistant to correction.
Recent research suggests that in the context of the refuted link between autism and vaccinations, current public health communications are unhelpful, even when they enlist facts to set the record straight.
Efforts to establish the truth might even be self-defeating, because they can increase suspicion and thus strengthen the very beliefs that they were meant to correct.
Such efforts are far more likely to succeed if they begin by affirming, rather than attacking, the basic values and commitments of those who are inclined to accept the theory.
Conspiracists like to say that the truth is out there. They are right. The challenge is to persuade them to find their way toward it.
Cass Sunstein, the Robert Walmsley university professor at Harvard Law School, is a Bloomberg View columnist.This article is adapted from the opening chapter of his new book, Conspiracy Theories and Other Dangerous Ideas. Sunstein is a former administrator of the White House Office of Information and Regulatory Affairs.