One type of deception, conspiracy content, is able to sell products on the basis that the rest of the world is wrong or hiding something from you, and only the demagogue knows the truth.

Anti-vax quacks rely on this tactic in particular. The reason they attack vaccines is that they are so profoundly effective and universally recognized that to believe otherwise effectively isolates the follower from the vast majority of healthcare professionals, forcing trust and dependency on the demagogue for all their health needs. Mercola built his supplement business on this concept.

The more widespread the idea they’re attacking the more isolating (and hence stickier) the theory. This might be why flat earthers are so dogmatic.