Orwell talked about this in one of his essays. The man who does not have fascism beating in his breast can't understand the pleasure of smashing someones have with a boot for all eternity. Sex, money and control have nothing to do with the pleasure of destroying others and their work.
Just like Hitler wrote (and proved), if you just lie big enough, people will be too "polite" to even suspect it a lie, and that works in many layers. E.g. for many wars, there is the outermost facade which is usually "we have to save X from the aggression of Y". Then there is "we meant well, but made mistakes" as the next layer, then comes "we didn't really mean well, it was about geopolitics and national power", then "it's not actually about national power, but about transfer of tax payer money to the military-industrial complex which ultimately has no ties to any particular nation, at the deliberate expense of social development".
And then you have the same game with the people involved in that, first there's how much they care for their children and are worried they might have to grow up without private jets, or how they're just trying to prevent a job someone would do anyway being done badly, and a whole host of other good reasons (maybe they simply operate a "business" and it "makes sense" to "make profit", no further questions). Then there's how they really just want power and fame, because we're all just apes and that's what apes want, and so on... but that they might simply be sociopath/narcissist and essentially stuck at some point in their childhood they built a shell around, that they might be merely a black hole chasing a fix they can never quite reach, now that is too much. Sure, we grant that it occurs here and there, but not as a major driving force, as the underlying pattern for a lot of things. No, of course it has to be more grandiose than that, if only because we're under the heel of and/or doing it.
It boils down to this, "normal" people aren't that way, simply cannot fathom the utterly alien and barren landscape some others operate in, and would rather pile on rationalizations and faux complexity. Even you described as "pleasure" which I would assume is more a temporary relief from the pain and fear of existence someone who never got to develop a personality feels constantly, and tries to instill in others.
TLDR:
> "I learned that it is the weak who are cruel, and that gentleness is to be expected only from the strong."
While I didn't put it that way, that's not the worst summary. Though I would say whatever induced his narcissistic personality disorder made him weak, and his disorder made him cruel. Lack of empathy and the inability to reflect are not strengths.
Hitler came back from WW1 with the same rank he went in, which was a huge disappointment for him, then he failed as an artist and ended up in homeless shelter where he was disliked because, well, I guess he just wasn't very lovable or interesting. He was driven by resentment and a feeling of inferiority, which is narcissism 101, as is the fact that he put on a great show which he and others fell for.
Generally, even when "just" talking about a sociopath desire for power and less about the self-destruction of someone as sick as Hitler: any leash transforms people on both ends, and the very desire to have power over others betrays a lack of inner strength and integrity. I can't prove that, but I'll claim it. And furthermore I think people pretend to themselves and each other that power is an end in and of itself, because they're so scared of what it covers up. When you walk on a landmine, you can't just go on pretending you still have legs -- not so with abuse, trauma and neglect resulting in a haywire personality development, where routing around things, in ourselves and others, is often our default reaction.
P.S. If you're really interested in the psychology of Hitler as well as the Nazis historically I can recommend the books by Sebastian Haffner, the titles make it kind of obvious which ones apply.
