I am generally very skeptical of AI doomsday scenarios but one thing I am worried about is some wannabe dictator telling an AI to do something that would be difficult for a human military to do.

You can't order an army of humans to kill every protestor in their way because eventually they run into their friends and families. An AI aligned with the commander will not object. And just like that, technology removes yet another point of friction that has kept human society somewhat in check.