Full spoilers follow for Supergirl.

Pretty much since the dawn of superheroes, one of the longest standing debates has been whether or not they should kill. Back in the day, vigilantes (even Batman!) carried guns, and coming from the “masked man” tradition, there wasn’t a lot of waffling about whether murdering a killer clown for the greater good was an issue. After all, it was a natural extension of the Westerns that had preceded them, with their good, their bad, and their ugly. But over time, that debate — both with readers and eventually viewers, as well as with the characters in the books, TV shows, and movies — has become a central facet of superhero lore. Should a superhero kill? If they kill, will they be going too far, thus losing their essential heroic nature?

Supergirl, now in theaters, dives head-first back into the debate with a plot that focuses on the title character (Milly Alcock) pairing up with a young girl named Ruthye Marye Knoll (Eve Ridley) who wants to kill Krem of the Yellow Hills (Matthias Schoenaerts) — a brigand, human trafficker, and piercing aficionado who murdered Ruthye’s entire family. Supergirl, meanwhile, wants to track down Krem because he has the antidote to a poison he used on Krypto the Superdog, and they now have 72 hours before the pup painfully dies.

Over the course of the one hour and 48-minute runtime, Ruthye swears she’s going to kill Krem while Supergirl repeatedly urges her away from that path, explaining that killing won’t make the pain go away; it will, in fact, ruin your life. There’s also a lot of discussion about the difference between being nice and being good, as well as perfect and kind… but all that gets thrown away when Supergirl murders Krem at the end of the movie.

To be 100% clear, this is less about the act of killing and whether that’s right or wrong than if killing a villain is supported by the movie that led to this act of extrajudicial execution. Supergirl’s whole character arc in the film is learning to let her actions match her words. She’s telling Ruthye that you have to stand for something, and that letting go of your pain — in the Maid of Might’s case, it’s the death of her own parents by kryptonite poisoning and loss of her childhood home, Argo City — isn’t an option; it’s how you learn to live with loss that matters.

When we re-meet Supergirl at the top of the movie, she’s partying under a red sun in order to dampen enough of her powers to stay absolutely wasted all the time, and struggling with finding a place she can call home. She doesn’t want to wear the “S” suit like her cousin Kal-El (David Corenswet), and she knows she can’t earnestly believe in people the way he does, because she wasn’t raised by good people in Kansas who are still alive. When she arrives on Earth, it’s too noisy, too strange, and doesn’t feel like home. Her journey isn’t about loving all this, but about accepting her destiny as someone who can inspire others to be better, even as she still has work to do on herself. She’s not perfect, but she can be kind, and she may not be nice, but she can be good.

At least until she stabs Krem… twice.

After throwing Krem far away from a fight and saving Ruthye from an attack by the villain’s Brigands, it’s clear that Ruthye has put her revenge aside and taken Supergirl’s words to heart. Meanwhile, Supergirl flies off to confront Krem, where he does a classic “you’ll never stop me, I’ll keep coming no matter what” speech. So Kara looks at him, stabs him as she says, “This is for my dog,” and then stabs him again straight through the throat, killing him, as she says, “And this is for the little girl whose life you ruined.” Not insignificantly, while this happens, Lobo (Jason Momoa) — who has been encouraging Ruthye to kill Krem in direct opposition to Supergirl’s influence — hungrily says “Yes!” in the distance as he watches on his space-bike. Basically, Lobo’s philosophy that “revenge=good” has won out in the end, not Supergirl’s philosophy that revenge doesn’t take the pain away.

Perhaps even more mind-boggling is the second line here, because so much of the movie is pushing back on the view of both Supergirl and Ruthye as “mere” little girls, as well as how they are not ruined: Their respective trauma is part of who they are and always will be. It’s not about being ruined; it’s about learning to live with the hurt and how it impacts your decisions that makes you who you are.

It’s not about being ruined; it’s about learning to live with the hurt and how it impacts your decisions that makes you who you are.“

This ending is also diametrically opposed to how it plays out in the source material for this film, the comic book Supergirl: Woman of Tomorrow by Tom King and Bilquis Evely. The graphic novel is told at least in part through narration by Ruthye, which we discover towards the end of the eight-issue series is a book written by Ruthye which she calls “fictitious fiddle-faddle” when Supergirl visits her about three centuries after the main events of the comic. This future-set scene takes place directly after Supergirl, whittled to a nub by their adventure tracking down Krem, explains to Ruthye that she was trying to teach her how to make the right choices over their adventures, but it didn’t work, so now she has to kill Krem. Ruthye shouts that she was listening, she did hear, and she did learn; they instead put Krem in the Phantom Zone, where he indeed learned his lesson over 300 years of imprisonment. Released at last, Krem begs for the older Ruthye’s forgiveness. Then she conks him on the head, seemingly killing him.

That in itself is a heavily debated moment of the book, but contrast Supergirl backing off killing in favor of reform at the end of that comic, and Ruthye (at least initially) choosing redemption over revenge. Funnily enough, we’re also told via that “fictitious fiddle-faddle” narration that Ruthye had Supergirl stab Krem to death with her sword, which we, the reader, know didn’t happen. So perhaps one could look at the movie as an adaptation of the book Ruthye wrote later, except that in the movie, there’s no narration, no future-set scene — just Supergirl impaling Krem and watching him bleed out in the dirt.

All of this calls to mind another highly debated, highly optional murder in a Superfamily movie — specifically, Superman (Henry Cavill) killing Zod (Michael Shannon) in Man of Steel. While far too much ink has been spilled about this already, it’s eerily similar to how things play out in Supergirl, with Superman holding Zod in a chokehold while he blathers about how Superman will never stop him, etc. Instead, Superman snaps Zod’s neck, killing him. There Superman feels pretty bummed out and screams, and the ostensible excuse is that this is a fresh-faced, younger Superman (who is 33) that hasn’t yet learned murder is bad. The argument in the other direction is that the whole point of Superman is to shove him into impossible situations like this and see how he does the right thing regardless.

That in essence is what Supergirl is trying to teach Ruthye — and by extension herself — throughout the newer film. She knows she’ll never be the nice dork her cousin is (Corenswet version), but she can find her own moral compass for good. So how does killing Krem satisfy that closure other than for movie audiences who would potentially be less than satisfied watching Krem get thrown into a rectangular prison?

Perhaps it’s something they’ll deal with further in the DCU, as the movie ends with Superman welcoming Supergirl back home to Earth and tentatively asking without asking if she’s okay. The DCU, too, has drawn the line between other heroes and Superman, with the Man of Steel stopping the Justice Gang from going too far in his self-titled movie, only for Hawkgirl (Isabela Merced) to gleefully kill a baddie while Superman is busy elsewhere in the climax. So maybe in the upcoming Man of Tomorrow, which also features Supergirl, we’ll see her either further inspired by Superman’s actions or breaking with him entirely. They’re different characters after all, despite the similar red-and-blue suits.

Just in terms of the movie Supergirl in theaters now, however, the title character’s final act in the film completely undercuts all the emotional development that has come before in service of a “hell yeah” moment in the theater. If anything should be killed, it’s the “should heroes kill” debate, because as Supergirl keeps stating over and over, death is never the answer.