Why? Because they:
Cause significant harm Form the backbone of many "populist movements" Foster and reinforce "exclusive worldviews" Reduce trust in public and scientific institutions
Which can in turn can:
Drive people to violence and even [gasp] Decrease people's desire to reduce their carbon footprint
That last one is a real reason for concern, isn't it?
Examples of conspiracy theories that UNESCO is super concerned about:
Climate change denial That federal elections in the United States were "manipulated" Michelle Obama is actually a lizard.
I have no idea where they got that last one, either.
This would all be cause for ðððĪŠ except that earlier this summer UNESCO released a report for teachers about conspiracy theories in the classroom and how to deal with them -- including "mediating" with parents (aka silencing them), when to report a student who refuses to budge, and more.
It may be 2022, but it sure sounds like 1984, doesn't it?
I'll tell you what "Reduces trust in public and scientific institutions": when those institutions repeatedly lie to you. That is far more dangerous than so-called "conspiracy theories"