Well said. To be clear, I agree with your outlook on human nature, but I try to check myself on not being optimistic to the point of ignoring people’s history. People do change, but we can’t presume in which direction that will be. We must remember improvement is a hope and a genuine possibility, but not an expectation. On the other hand, Orwell is regarded as insightful for good reason but of course he is also very cynical about people and the future.
A catspaw is just a term for someone who is used as a tool of another to their detriment. It comes from a French fable where a monkey convinces a cat to grab some roasting chestnuts for them to eat, but the monkey eats them all while the cat ends up burning its paw.
Edit: This is the fable. https://en.wikipedia.org/wiki/The_Monkey_and_the_Cat
Tropes can easily become cliches if done poorly, but in essence they’re just common concepts in storytelling. The idea of having a protagonist struggling with finding what lines they won’t cross, and accepting what consequences result, can make for a really compelling internal conflict. And having a no-kill rule is often a practical one for longer series in particular.
Imagine if Batman’s rogue gallery couldn’t be re-used unless the writers had them always be able to get away when their plans are foiled. When Batman instead sends them to jail, they can be shelved for a while without making Batman look very selectively incompetent at actually catching criminals. Instead, it’s justified as a principle that he upholds, while giving the writer opportunities to also show character growth for villains. And if you argue he should focus on the greater good by permanently eliminating threats, then it can be viewed as a character flaw that gives him depth.