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.

It’s Cold War propaganda.

Literally “Animal Farm” in a single sentence.