I think 9/11 is the limit of people being able to understand things. Too easy post-9/11 to fool enough with junk nonsense theories and too many crooks and grifters and dishonest media to ever be able to relegate the idiots to “the fringe” anymore.
Too many like Hankins, living a lie/fantasy online on other people’s money.
Many feel the government/Deep State itself poisons the well and inserts various conspiracy theories into the debate so that many dismiss
all conspiracy theories, real conspiracies, as kookery

These people claim the term "conspiracy theory" was actually coined by the CIA through a conspiracy LOL, as a term with which you can dismiss off hand all even legit criticism of the official line.
But I agree with you largely. Like people were willing to believe directed energy weapons in the case of 9/11, nanobots in the vaxx or exploding mike and Egyptian planes in the Charlie Kirk killing. When real conspiracies should be enough, like the population replacement conspiracy or the Jewish control of US foreign policy, as Nick Fuentes has been saying. With 9/11 IMO there have been several related conspiracies though, no need to grab onto ridiculous stuff like the planes being holograms.
My idea is to always ask how many people would necessarily need to be involved in a given conspiracy and could they all keep it secret?