I recently listened to this Behind the Bastards podcast about the origins of anti-semitism. There's a lot of dark and informative history to learn from. It centers on a plagiarized-of-plagiarized document that is extremely anti-semitic - 'The Protocols of the Elders of Zion' (TPEZ here on out). Produced in Czarist Russia (likely by the secret police, the Okhrana), it has become the bedrock of pulp anti-semitism. The document is osensibly the minutes from a meeting of jews who are plotting to overthrow the monarchies and institute a new world order. Sound familiar? That's because the document basically outlined modern anti-semitism. The thing is, most of those who exploited it realized it was a fake - the Nazis never explicitly used it, for example, because they could see it wasn't something credible to attach their brand to. But what they did say was 'even if it's a fake, its internal content is true'. That is to say, they acknowledged that it was a fake, but because their whole ideology was about fearing that jews were gonna take over the world, they took the content of the fake to be true. And so they indirectly would promulgated it through the more ruffian-branches of the Nazi party. As Behind the Bastards notes, it wasn't something anyone would actually read - it's too ridiculous - but something you would throw into conversation or cite in anti-semitic propaganda to give your argument more... 'credibility', I guess.
Being anti-semitic was quite the fashion before the Nazis showed how horrific it really was. Even before modern anti-semitism took form, Jews have always been highly discriminated against. In the Middle Ages, Jews were often kept in ghettoes, to live by themselves, and often subject to mass killings. Conspiracies spread that Jews would steal Christian babies and do rituals with them and their blood (there is no evidence indicating this ever happened, to be clear) - in fact, there still remains religious art (such as stained-glass windows) depicting Jews extracting blood from Christian babies, or Jewish babies suckling from a pig. Fast-forward to the future, TPEZ explodes - and it ain't just Nazis who don't like the Jews. Notably, Henry Ford distributed hundreds of thousands of copies in the US, and the text caused a huge stir in Colombia in the Great Depression era. 'Behind the Bastards' discusses how, in the throes of the global economic tailspin, the Colombian conservative party found new life in TPEZ - even as it was a known forgery (again, that 'it's a fake, but the internal content is true'). They believed the liberal party was conspiring/controlled by Jews, and so they were not just a political opponent, they were a threat to the state. Sound familiar? Colombian government broke down, because well, one side was mired in an unfounded anti-semitic conspiracy. This then boiled over in 1948 when the Liberal presidential candidate was assassinated, sparking rioting and outrage. For ten years, the nation was in civil conflict - this period known to Colombians as La Violencia.
You might now notice a lot of parallels with modern right-wing conspiracies in America. For example, there is a general fear of George Soros in particular who are sewing disorder and chaos - but why not other billionaires? Or you'll hear the QAnon fears that pedophiles are doing satanic rituals with children, and the liberals are in on it, and only DJT can stop it. Or you'll generally hear of 'globalists' who are trying to destroy Western values and all of that. These aren't just 'crazy ideas from nowhere' - they are cookie-cutter ideas embedded in our culture by centuries of anti-semitism. They aren't just harmlessly goofy - they draw, quite explicitly, from a long and bloody history of hating, oppressing and killing Jewish people. As we look to history to see how these crazy ideas play out (which might at first appear so stupid as to be harmless), we must realize how grim this conspiracism bodes.
Quick sidenote - attacking 'globalists' might sound like it's a critique of capitalism! It's not. The left-wing position is not that capitalists are essentially evil people conspiring to destroy the world (had the dice been rolled slightly different, Bill Gates would probably just be another regular guy (he seems personally nice tbh - and I'm salty about Microsoft/Linux!), not an evil psycho), but that Capitalism leads to the accumulation of power in the few, who exploit the labor of the masses. While left-wing politics does not exclude being very angry at capitalists, the capitalists do not maintain power through a grand cabal, they maintain power for structural reasons. Furthermore, it doesn't matter the background of a capitalist - while there may be local dynamics and history outside of capitalism (ie a group that has traditionally been the ruling group is now the local bourgeoisie), leftists don't concern themselves with evaluating if a type of person has a proclivity to power. This is frankly absurd and dangerous thought, and leftists would be happy to have every kind of person live happy and well. So be very careful - don't fall for 'the globalists' type of propaganda!
Back on track, my point is that anti-semitism and TPEZ has outlined what an unfounded conspiracy looks like - it gives the tropes to build such a conspiracy out of. But the problem is, the more evidence you bring to a conspiracy theorist, that will either (A) say it's fake, (B) bring up something totally new ('gish-galloping'), or (C) just shut down the conversation and say you're either a sheeple or you're in on it. That is to say, trying to use evidence to convert a conspiracy theorist is like trying to win World War I without the Mark V tank. Maybe it's possible, but is it the best way? History seems to imply that it's not.
So then how on Earth do you fix it? You have to identify what drives people to believe this stuff. Some people are, well, kind of hopeless. But some of this can be fixed by fixing material conditions. People believe this stuff when the world is collapsing around them - in the States we have collapsing infrastructure, growing power of tech giants, a government that seems incapable of doing anything, drug problems, police violence and protest, and so on. All of this is a symptom of our system being totally paralyzed. When the system breaks, people look for reasons it's broken. If the system isn't broken, that motive withers. Look at the United States under Franklin Delano Roosevelt. Now anti-semitism was still there (hello Henry Ford!), but it didn't metastasize to critical mass, it didn't rip the nation apart. As a nation, rather than relying on fear, hate and anger to drive politics, we came together as the New Deal gave Americans work opportunity, brought them electricity and hope, and empowered workers to unionize and have a say at their work. This is another point - If you actually allow people's voices to be heard democratically, they are less likely to believe the system is rigged and that some puppet-masters control everything. Being able to voice your thoughts, at the ballot box or through a union, and actually see that have an impact, well, that kind of defuses the idea you don't have a say in things. Democracy in both the Republic and the workplace can go a long way here.
To people who don't believe in the conspiracy theories, we may wonder why people can believe in this foolishness when the evidence is quite clear that there isn't such a thing. We are inclined to think that these people must just be uneducated. The solution isn't more facts, fact-checkers, bla bla bla. These are good tools, but they aren't the solution. This is because conspiracy theories emerge when everything seems to break down, and people are looking for someone to blame. Most of the time though, things break down not because people made it break down, but because they failed to stop it from breaking down. An error of failure, not an error of malice. But when people are angry and scared, this doesn't cut it. The only way to defuse conspiracism is to fix the system - give people work, give people hope, give people resources - like the New Deal. As history shows, if you don't fix the system, conspiracies can help break it down. To properly address conspiracies, we must properly address their cause.