It’s the Great Pumpkin, Charlie Brown is a cautionary tale about cult behavior and the pitfalls of religious psychosis
Linus, the erstwhile voice of reason (think Charlie Brown Christmas where he quotes the Bible and expostulates on the true meaning of Christmas) is somehow completely delusional when it comes to Halloween and the coming of the Great Pumpkin. He seems to have entirely fabricated the legend and lore of the Great Pumpkin. He sacrifices everything a child can sacrifice-candy, fun, Sally’s admiration-to wait in the pumpkin patch on Halloween night. And he’s under the impression that the most sincere pumpkin patch will be the chosen one (sincerity being a proxy for faith?). Then, when the Great Pumpkin turns out to be Snoopy, he refuses to listen to reason and see the error of his ways. Candyless and socially ostracized, he refuses to concede the non existence of the Great Pumpkin and he vows to return the following year.
My extremely low stakes conspiracy theory about Its the Great Pumpkin Charlie Brown (1966): some Peanuts writer had intel about MKUltra and used the Halloween special as a vehicle to covertly warn the public about the dangers of mind control, group think, cult behaviors, and late 60s drug culture