Having claimed that a Supreme Court justice may have been rubbed out, that the Pope is Mexico’s patsy, and that the president of the United States wasn’t born in the United States, Donald Trump has made political conspiracy theories seem like a unique speciality of the American right.

If only. Crank theories are far-flung, geographically and ideologically. They land wherever chaos and confusion reign (that’s anywhere), and on whatever side of the spectrum populists reside (that’s both sides).

As populists proliferate throughout Western states, we can all look forward to learning more about the various pernicious forces that clandestinely govern our lives. It’s just not clear how societies should respond to ridiculous ideas.

None is immune. In France, the founder of the extreme right Front National claims the Charlie Hebdo attacks were enabled by Western intelligence agencies in collusion with the French government. In Poland, the leader of the nationalist governing party believes his brother was killed in a plane crash by assassins, not pilot error, and that the country is being manipulated by the European Union, the Russians, the Germans, the refugees, and other "gangsters." And in the United Kingdom, the socialist Labour leader and presumed Da Vinci Code fan fiction author thinks Illuminati members are building a New World Order.

Maybe because they’re so patently ridiculous, conspiracy theories often are less reviled than hate speech. They’re more existentially dangerous, though. Like his xenophobic pals, a conspiracy theorist targets a group — any group, many groups — on which to pin his anxieties. But the conspiracy theorist doubles down.

The crackpot attacks the whole of society. He demands a coherent explanation for the bedlam of life and he finds a satisfying one in the spectre of a sinister, shadowy entity who’s in charge of it all.

By his account, events don’t merely occur; they are orchestrated, often through the infiltration of political parties, the media, the academy, the banks, or Hollywood.

This explanation suits many populists. They’re deeply suspicious of elite institutions anyway. And institutions — any institution, every institution — are automatically suspect when a nebulous consortium of super-villains is pulling all the strings.

So democratic societies and their institutions have a clear interest in debunking crank theories. But how do you argue with people who think the opposing argument is rigged? If there’s an answer to that question, it probably will be found in how conspiracy theorists think.

Typically, they trust a few segregated sources of information. Harvard scholar Cass Sunstein finds conspiracy theorists join isolated communities of like-minded paranoiacs, confirming and amplifying each other’s biases, striving for the mantle of Most Suspicious, and monitoring the beliefs of other group members for signs of dangerously reasonable positions. And what if elites occasionally single out a particularly egregious theory to disprove? Conspiracy theorists think they doth protest too much.

Since political conspiracy theories defy standard argument, some people recommend the most harmful ones be banned; others, such as Sunstein, suggest governments infiltrate conspiracy theory networks, possibly covertly. But these proposals confirm the darkest suspicion of all populist conspiracy theorists.

Any open society’s best defence against conspiracy claims must be more openness, not argument by stealth, and more regular public rebuttal, not speech bans. Strengthen the actors that hold politicians to account, the rules that keep government transparent, and the research institutions that deal in factual information.

I’ll grant you, this answer isn’t satisfying. Reasonable answers rarely are.

Shannon Gormley is a global affairs columnist.