people respond to incentives.

that's all you need to know.

take the good and the evil, the smart and the stupid out of it, and it will make a lot more sense.

most people would be just as 'evil as who you are talking about given they had the same levels of power. you false belief is that these people 'in power' are somehow superhuman and can resist the temptations and abuses that come with the power they have... they can't, and don't, and most folks are like that. it's exceptional when someone doesn't abuse their power.