Originally Posted by
The Beast
It depends who is doing the interpreting. Most comic book fans who go into the movie to evaluate it based on accuracy to the source material but movie fans don't. They have their own expectations and one of them, more often than not, is that the villain must die. So a clash of tropes ensues and a filmmaker has to choose which audience they are going to aim for. It not a mistake or they didn't get it right if they chose movie fans over comic fans because it's a Movie first and foremost.
There's no logical reason for super heroes not to use lethal force if the situation warrants it. The no kill rule is a throwback to 1950's McCarthyism/Werthamism, ultra-conservative values imposed on comic books when they were solely children's entertainment. Times have long since changed and comic books are adolescent power fantasies again so there's nothing wrong with Superman using lethal force every once in a while against unstoppable foes.
Every time I see a superhero refuse to kill, it ruins my suspension of disbelief because I know the only real reason they have is children may be watching from the other side of the 4th wall. I've felt this way ever since I was 14 and fortunately CoIE, DKR and Watchmen came along or else I probably would have stopped reading comic books 30 years ago.