That is the question worth focusing all the available energy and enthusiasm that is always somewhere else, but never at the humankind's worst problem.

I think the answer could arise from a widely growing understanding of

a) the methods of mass manipulation. Without manipulation, or outright mass hypnosis, no dictator is possible;

b) the whole structure of power, and the fact that there are numerous barriers to filter out all non-psychopaths along the way to the top, with multiple checkpoints where an ever increasing degree of corruption and depravity must be demonstrated to the controllers.

But even a) alone should be sufficient.