I actually know someone who got sucked into the flat-earth conspiracy theory. He's an intelligent, seemingly rational guy, and I couldn't for the life of me understand how it happened. He immediately got emotional and angry when talking about it, so I just avoided the subject altogether. The flat elephant in the room.
"At YouTube, I was working on YouTube recommendations. It worries me that an algorithm that I worked on is actually increasing polarization in society… The flat-Earth conspiracy theory was recommended hundreds of millions of times by the algorithm. It’s easy to think that it’s just a few stupid people who get convinced, but the algorithm is getting smarter and smarter every day." – Guillaume Chaslot, The Social Dilemma