Why does Superman get a pass for murdering a depowered Zod in Superman 2?
Old movie and Superman not being in the public consciousness enough for people to care.
As
@Quarterback Rex Grossman pointed out, no one cared for Keatonman killing. I honestly don’t believe anyone cared about Batman killing till BTAS and Nolan became the primary sources for most people. They hammered in the rule and since the general public views them as their Batman, it is hard to break away.
By contrast, no one cares about Superman. Sadly, STAS gets sidelined because of the shows surrounding it (sad as it is more consistently good), and none of the films left the same impact as Batman. At best, Superman is characterized by his crossover appearances like LEGO Batman, which is why Injustice did so much damage to him. At the very least, he is better than Wonder Woman who is horridly mischaracterized as a cold-blooded killer thanks to Injustice and terrible comics having panels posted around - that infamous, there is a reason I have no villains being a big example.
He should have a "No Kill" desire.
Keep the JLU characterization where the man gives zero fucks if it is Darkseid and maybe Luthor. I think Supes being ready and willing to stomp Darkseid’s ass into the pavement upon just seeing him makes a lot of sense.
Generally, the more angry Clark of that universe is probably the best way of going about it. He clearly still values second chances, but he also has a much more defined boiling point where he will take drastic action compared to the rest of the League. Makes sense the guy with the weight of the world on his shoulders is a little more willing to “do the needful” and remove potential escalations compared to his colleagues.
Don't get me wrong, I am not a purist or similar.
But for me personally it has always been hard to see Batman's no kill as a real moral standard instead of cynycal attempt by writers to justify why his very profitable villains are still around.
Was even more ridiculous with Batfleck. You have to wonder that if his Batman is willing to kill then why is his Joker still alive?
In general, superheroes are children’s characters and made to uphold ideals. The idea of second chances and pushes to make people better are noble and of real value. BTAS is well loved because they show the complexity of evil and that not all people who do bad things are necessarily just in it to hurt others or that there may be fundamental issues in society that can create a monster.
I think a large problem is the adult works now go overboard with how ridiculously evil characters are to the point where the message of redemption is hard to swallow. Injustice wanting me to believe Superman took a step too far in killing Jonkler after he nuked a city is utter insanity. Lex having a little tard smack down with Superman should not be put on the same tier as Darkseid ass raping a planet and killing untold billions, yet comics want to treat both crimes with the same resolution.
The DCAU worked because villains never got too out-of-hand outside of rare circumstances, and of course, when those circumstances happen, we get Jonkler getting shot in the heart, Lex getting a laser through the head, or Superman just curb stomping Dankseid with no mercy. It was way more realistic in how these things should be handled.