Queen Michael said:
Okay, we all know what people who dislike Man of Steel hates the most about the movie. Superman kills a guy, even though that's something Superman isn't ever supposed to do.
But here's the thing: Almost every iteration of Superman that I know of has either killed or tried to kill somebody at some point.
Here's what's different about MoS Superman: He kills the bad guy during his very first superhero adventure. Zack Snyder probably intended the scene to show Superman being forced by horrible circumstance to break his most cherished principle. But since we've never seen a Superman adventure where this Superman doesn't kill, and he shows about ten seconds of angst about it, he comes off as a Superman who will kill whenever it's useful.
And then he kills the villain in BvS too, and firmly establishes himself as a Superman who kills in every movie.
That's the problem with DCCU Superman. Not that he killed a person. But that he was so damn eager to do it.
The point of Man of Steel was that Clark HAD no rules yet, because as you said it was his
very first superhero adventure. However one thinks how effectively they were showing it, the movie was supposed to show Clark growing into a hero, not having powers and just deciding to be one with a predetermined moral code and motivation to help people as most versions of Superman just do right off. That's why Clark is spending the first half of the movie wandering the Earth, doing things like wrecking a bully's car one minute and saving the people on the oil rig the next, he hasn't really decided whether he's going to spend his life saving the world or just live his life minding his own business while occasionally using his powers selfishly. Papa Kent's role is that he's supposed to play devil's advocate for the typical Superman mythos, to show Clark that he doesn't owe the world anything and to keep himself under the radar because Papa Kent recognizes how the world will seek to exploit or destroy Clark simply because he can do what he can do. It's Zod's arrival and subsequent events that really kicks off Clark's development into a hero, that makes Clark recognize how he can no longer sit on the sidelines and that he must use his powers responsibly.
The problem is that viewers have these preconceived notions about the character, which as you said isn't even all that accurate, that Clark Kent shouldn't be allowed to develop into Superman, he should just be this perfect little Big Blue Boy Scout right out of the box and never, EVER ever!!!ever!!!ever!!!ever!!!ever!!! kill under any circumstance no matter how justified or unavoidable. The fact is, even without the neck snap scene there is literally NOTHING else Clark could have done besides kill Zod at some point, the neck snap scene is just the first point when Clark both had the opportunity to kill Zod during the fight and people in direct danger to force his hand. Zod made that more than clear he was never going to stop until he was either dead or every single human on Earth and Clark was. Even if Clark was experienced enough with his abilities and could take Zod out non-lethally there is no facility on Earth that could contain him and if they tried Zod would just break out in a manner of seconds and go back to rampaging. Zod wouldn't be stupid enough to get trapped in the Phantom Zone again either, assuming Clark even knew how to put him in there. People complain about Superman killing and the massive destruction of Metropolis, but they fail to recognize there's no other way things could have gone. This wasn't some battle hardened Superman fighting some superbeing a level or 2 below Superman with the experience and superpower advantage behind him needed to effectively control the fight or move it so damage to the surrounding area is minimal. This was a green as a cabbage field Clark Kent desperately trying everything he could to stop someone who was just as powerful as he was, who could not be bargained with, reasoned with, or captured. Zod was both determined to destroy the world and not stupid enough to fall for anything Clark could have done to get Zod out of Metropolis and if Clark tried Zod would have just stayed at Metropolis and destroyed everything. Clark's anguish over killing Zod is supposed to be the catalyst FOR the "No Killing Rule," now that Clark actually has blood on his hands.
All this development ties in nicely with Dawn of Justice on Superman's side at least. Superman (who I now refer to as such because he actually is now) tries to inspire people, to work with the government and authorities for his heroics and to answer for the destruction he unavoidably caused during the first movie, all curtailed by Lex Luthor's efforts. Superman now shows a severe aversion to killing most effectively demonstrated with his aversion to Batman, who had just started killing people willy nilly, while Superman attempts to get him to stop and talk Batman down on multiple occasions both before and during their fight, which as he said if he wanted to hurt Batman he could have done it 5 seconds into the fight.
On a side note, Batman himself is shown in the movie to have been operating for years at least long enough for the events of something similar to Death In The Family to have happened. He's become so broken by everything he's gone through that he's stopped pussyfooting around with criminals and just resorted to killing them, with marking those he can manage to capture alive so that he technically doesn't kill them as a justification in his mind for doing it. This would have probably worked a lot better if we had a couple movies to establish this Batman's character especially his own "No Killing Rule" and to give him something that would break him so completely that he would subsequently abandon it in Dawn of Justice. Ironically unlike with Superman Batman didn't get the time needed to develop and the writers tried to cram everything about Batman's character and subsequent change in said character into one movie while expecting the viewers to fill in the blanks, which is where things failed with Batman in Dawn of Justice. Having to cram all the establishment and development of a character into one movie is why each character needs at least one solo movie or multiple bit parts in other movies before they start throwing them into a team or Vs movie.
Of course, I'm probably overthinking this, but that's what threads like this are for I suppose.