Update: I was wrong. The first meeting will be this Sunday. I posted these links to the fanclub FB page to get people interested:
https://bookofbadarguments.com/?view=allpages
https://www.smashwords.com/books/view/100799
(note: by far most of the fanclub members are fluent in English)
I think I have come up with a way to make the themes interesting to them. As they already love Harry Potter, they're not afraid to use complicated Latin phrases. So I can say something like, "The key to casting a successful Modus Ponens spell is to first summon the Antecedens and then proceed to the Consequens. Never summon Consequens first, as it will cause the spell to blow up in your face." Then we can study some defensive techniques against the Ad Hominem curse.
At my local Harry Potter fanclub (Bogotá, Colombia) some members teach "classes" on subjects they're passionate about. We've had informal courses on history, creative writing, English, etc. But recently some other classes have appeared that have made me worry seriously: astrology, divination, ancient runes, and all other sorts of nonsense. They're not taught as folklorical pieces of the past, but as serious practices that are supposed to actually work. I think this is particularly dangerous for the small kids that comprise the majority of the fanclub and still need help learning that magic doesn't exist.
So I proposed the fanclub chief that I could teach a Muggle Studies class: logic, critical thinking, philosophy of science, etc. In two weeks we'll have our first class, and I intend to begin talking about the most common biases. I already downloaded this website's PDF guide to holding a Less Wrong meeting. Aside from that, what can you suggest for a successful Muggles Studies course?