|Four white kids killing a black(ish) guy? He probably had it coming.|
Every now and again someone will decide "hey, it doesn't make any sense, so fine, let's let a superhero kill some people." Maybe they give Bucky Barnes a gun while he's acting as Captain America so he can shoot some AIM henchmen. Or they'll make Wolverine an Avenger and turn him loose on some villain group. Or Superman just starts wiping out Parademons without even really knowing what they are.
For the record, I really, really hate the relaunched Justice League book.
But anyway. Here's the issue I see.
With a character like Superman, you need to have that clear-cut "all life is sacred" mentality. When you have someone who, at times, is able to actually push around the moon or stand up to God-like beings, the idea of him not wanting to keep everybody alive makes him rather scary. If there's a being out there who just wants to keep everybody safe at any cost, that's comforting. There's a protector out there watching out for all of us, and won't take the punishment of someone doing something wrong into his own hands. He's not the judge, jury, and executioner, he's just the barrier preventing a person's choices or mistakes from getting worse.
Now, change that to a guy who's willing to say "well, hell, you're a soldier, you had to expect this was coming" and simply slices you in half with a truck.
That's terrifying. That's taking a protector and turning him into an authoritarian figure who has essentially set himself up as the final word. That's borderline super villain right there.
Another example is Captain America. The thing I love about Cap is he's stronger, faster, and more agile than 99.999999% of humanity thanks to the super soldier serum. However, he doesn't charge into battle against bank robbers with a sword or an AK-47. He carries a shield. He, like Superman, is a protector. He didn't join World War 2 raring to kill Nazis, he wanted to stop people from doing horrible things to other people. There's a huge difference there.
When Bucky took over and started carrying a gun, that twisted the entire archetype around, so you had the symbol of American freedom now going around not just with a weapon, but one that could kill from a distance. Maybe I'm wrong and it only shot rubber bullets, but I seem to recall him gunning down a bunch of henchmen at times and also firing bullets at other bad guys.
I could go on about a lot of superheroes who make "no killing" their code. Hawkeye, in one of my favorite moments involving the character, broke down to the Thunderbolts about why they don't kill (this was, of course, before he decided to try to murder Norman Osborn).
Batman (despite carrying guns and killing people back when he was just a rip-off of The Shadow) seems to have based his entire concept now on a childlike mentality of "I can stop Crime" and "nobody will be murdered again." Iron Man has actively gone out of his way to destroy old equipment of his and weapons made by his company because he doesn't want to be even indirectly responsible for more killing. There's Spider-Man, whose entire concept boils down to "when you have amazing abilities that make it possible to help people, you don't abuse it."
You'd think they'd come up with a snappier catch-phrase.
Now, does that mean heroes should never kill? Well, no, but when they do have to take the "final solution" it should actually mean something, not just be "okay, he's dead, I'll feel bad about it for this panel and then next issue never think about it again." The first time Superman took a life in the 80s (killing three Phantom Zone villains) it broke him. He actually developed a split personality and dressed up in armor and went around beating up thugs with nunchuks.
At times, I will admit, it will become necessary for a superhero to take that final step to save a lot of people if there's no other choice. And I don't mean the cheap way Man of Steel did it where "oh, I have to kill Zod because the writer is too lazy to think of something," but because there's actually no choice. Captain America fought in a war against great evil, it'd be foolish to think he never had to take a life to save others. Thor probably had to kill trolls to save some innocents because there was no other option. Wonder Woman killed Max Lord because of his control over Superman and didn't want her dear friend to wind up with blood on his hands. Flash killed the Reverse Flash, but to his credit it was an accident.
But more than anything else, I think it holds super heroes to a higher code. We expect them to be the best of us, otherwise, as I said before, they're rather terrifying. I wouldn't feel safe in a city if I knew the Punisher was running around gunning people down and causing explosions, there's no way to make sure there's never an innocent civilian around who won't get hurt. If the only heroes around were the ones during the grim and gritty 90's (you know, when VENOM was considered a hero ... the first time, I mean) I'd be scared to leave the house.
We have rules keeping police and federal agents from simply shooting anybody they want to without justifiable cause, and when you live in a universe with web-shooters, adamantium shields, healing factors, metal suits of armor, and Hulk-level strength, it shouldn't be that hard to come up with a better solution. I think it's a lazy writer who simply decides "oh, well, there wasn't a choice, so let's move on."