For about ten thousand years now, human societies everywhere had haves and have-nots. Transition from have to have-not could be swift and brutal. The thing that you stopped having could be your wealth, or your liberty, or your life. Transition from have-nots to haves was an arduous process, most times multi-generational, and most times unsuccessful.

In such societies, survival required alliances, sometimes side switching, and most surely secrecy, misdirection and deceit. Conspiracies were the rule, not the exception. Actually there were no exceptions, there were only conspiracies everywhere.

The ability to guess what's going on was then a huge advantage, and you bet evolution has selected for that. Could evolution have erred on the side of being too trigger-happy? Little doubt about that. Innocent until proven guilty, benefit of doubt, right to due process, habeas corpus, etc, were all luxuries that few could afford until very recent times.

The fact that some people believe in conspiracy theories should not puzzle anyone. This is our natural state. Education and culture is how you exit this natural state, but even then, you are never completely immune to believing a good story. At least I know I'm not. Maybe I'm in a minority...