To define someone as bad you must also define good - and if you are defining the terms, they are meaningless.

From the perspective of the "bad men", they are serving good - be that the good they see in themselves or whatever cause it is they act in. Stalin genuinely believed he was acting in the interests of the Soviet people. Pol Pot was liberating his countrymen.

I would argue that the GP's interpretation is correct - we willingly ignore our own moral compasses when we examine the behaviour of the powerful, as to admit that those that hold power over you are "evil" is to admit your own weakness in not actively opposing that power - so power does indeed corrupt those who behold it, as much as those who hold it - if not moreso, as the "bad men" act in "enlightened self interest" and do no wrong in their own eyes - but you do do wrong by knowingly averting your eyes.