*Shrugs* At least X-Men came up with an explanation/ "plausible" way of doing it...
On the thread, there are just too many, most have been said.
A hero not taking out a villain who's killed thousands because "they won't be any better than them". This is the one that probably gets to me the most.
Especially as there are other ways of stopping someone without killing them. I mean if you've trained all your life in martial arts and other skills (like anatomy)... surely you can break "every" bone so that they are paralyzed and whatnot without killing them.
Everything said on Batman. Which is why I prefer all the other versions we've got over the last couple of years - Imposter, Earth One, Murphyverse, Grave - and I recommend (traditional) Batman fans to go read them.
The reality is that we readers have to take things with a pinch of salt as there are certain things that just won't happen due to the need for Publishers to continue telling stories and making bank...despite the fact they don't make a lick of sense.