I’ve always thought one of the main practical problems with conspiracy theories (and conspiracy theorists) is that they make an effective response all but impossible. ie they are fatalistic and disempowering. This isn’t a knock-down argument against their truth, but shows how they can serve, or give succour to, those whose interests are bound up with the maintaining the status quo. This is a good reading of why they are so prevalent at the moment:
Beneath Conspiracy theories, the class war (NewFrame)