I'd say that the mighty of this world most likely aren't demons themselves, but rather possessed by some malicious (or just slightly insane) spirits. However, some of them might've signed a pact with otherworldly forces beyond their comprehension. The oldest trick in the book: they've obtained an immense power, indeed. But pledged their soul in return...
Don't we have more than enough demons on the planet already? I mean just look at some of the so-called "world leaders." I'm all for putting curses (not just verbal) on those a-holes.
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