To popularize the use of psychedelics to the general public? Because that's what he did. To promote illegal activities? Because that's what he did.

Yes, that's about the argument of Jan Irvin. That the counterculture was encouraged and propagated to a certain point by such an entity as the CIA for the purpose of debasing the values of society. He would call ideas such as the one being put forth in The Sacred Mushroom and the Cross by John Allegro as weaponized anthropology. It's well known that the CIA has been involved in drug smuggling, in mind control experiments, and in the entertainment industry. So I don't see why thinking Mckenna getting off scot-free after being caught doing something illegal, while supposedly being a threat to the authorities, and then making ambiguous jokes about him being recruited by ''they'' (note that FBI is something like seven sentences closer to ''they'' than the word alien) could only mean that ''conspiracy-minded people'' are silly/dumb, for that the misinterpretation would solely fall on them. In this case, I think the responsibility​ of discombobulation rather falls on McKenna.

B.t.w., I forgot to mention that I don't​ think McKenna's ideas about the concept of a ''mother of all conspiracies'' (that's what it is because whether​ people like it or not conspiracies do exist) and the possibility of him having been entangled in some intelligence​ apparatus aren't mutually exclusive. Both make sense to me. :-)