Hmm. [Opens mouth to speak, nothing comes out.] Hmm.
Before I start, a caveat: I couldn't help but notice the controversy over Man of Steel on Twitter, much of it involving Mark Waid, one of the standard-bearers for a view of Superman I share. Passions are running hot over this one, which is both good and bad—it's good that people are talking this much about a Superman movie (or a DC Comics movie in general), but it's disheartening that they're arguing over the fundamental nature of a character that should be well established by now. Anyway, I've avoided reading any reviews or commentary, so other people may very well have said what I'm about to say, and if so, likely much better.
I'm going to offer some general comments about the movie, and then some discussion about some ethical topics raised by it. I'll keep the spoilers until the second part, and I'll warn you when they're coming.
First, Man of Steel as a movie (not as a Superman movie): I liked it. I loathe long films—90 to 100 minutes is perfect as far as I'm concerned—but even at 143 minutes it didn't feel long, and no parts of it dragged. Henry Cavill impressed me as Clark/Superman, having only seen him in The Tudors, and Amy Adams (whom I've seen in most everything she's done) played an effective Lois, but neither blew me away. The finest perfomances by far were Russell Crowe as Jor-El and Michael Shannon as Zod—both stole every scene they were in, and interactions between them were marvelous to watch. (The filmmakers cleverly found a way for Jor-El to appear throughout the movie despite... well, you know.)
The action scenes were spread throughout the movie nicely, broken up by emotional dialogue or flashback. This was important, because the action scenes themselves were intense—while there was little blood, there was more than enough destruction and explosions to earn the PG-13 rating. (I would not be comfortable taking my kids, 5 and 10, to this movie, and they've seen all the recent Marvel superhero movies.)
Visually, the movie was very stylish. While the Smallville and Metropolis scenes were by necessity reminiscent of past depictions, the designs of Krypton and Kryptonian technology were breathtaking, from their 3-D sculpting technology (for lack of a better term) to the armor the Kryptonians wore on Earth. But the movie was just so dim, like it was all shot through a fine gauze. There were no bright colors at all: Krypton was gray with accents of gray. Smallville was brown. Metropolis was—guess what—gray. And if you thought Superman would bring a ray of sunshine into any of this, you would be wrong. We've all seen the movie costume, all muted red and blue, with just a touch of muted yellow thanks to DC Comics' New 52 redesign. (And don't even get me started on the costume's texture, which reminds me of that rubber thingie you use to open the jar of pasta sauce that's been in your refrigerator since Superman Returns was out.)
But the dull tinge of the movie matched its narrative tone well—this is a dark movie through and through. Not quite Nolan-Batman dark, but more like Webb's Spider-Man but with none of the humor. The team behind The Amazing Spider-Man was able to give us a superhero film starring an upbeat character that fit with the current times but still retained some of the irreverance we expect from Webhead. But Man of Steel, featuring a character whose big red "S" stands for hope, was sorely lacking in hope, optimism, or joy. This is definitely a movie for a generation that is more likely to look in the sky and say "it's a bird, it's a drone—yep, it's a drone" with little hope of seeing a hero.
And nothing illustrates that point better than the ethics-loaded notes in the movie. This is where the SPOILERS start, so read on at your own risk if you have yet to see the movie.
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I have very mixed feelings about how Man of Steel showed Superman's heroism and ethical decision-making. Don't get me wrong, there are several inspiring scenes of heroism in the movie, such as the scene from the trailers in which young Clark pushes the schoolbus out of the river (at the risk of revealing his powers), and the scene near the end of the movie in which he destroys the world engine while it robs him of his powers. Other characters get in on the action too: Lois, Perry White, and Jonathan Kent all get chances to be heroic. These were fantastic moments in an otherwise dour film.
Unfortunately, these moments we expect from a superhero movie are overshadowed by other scenes that we don't. Clark/Superman makes some questionable moral choices in the movie, choices that may be understandable if any other person made them, but not Superman (or even any other cinematic superhero outside of Wolverine).
I've written a bit the last couple years about Superman's need to use moral judgment, rather than his incredible powers, to resolve tragic dilemmas, conflicts in principles or duties from which he cannot excape "with clean hands." In the comics, this usually takes the form of Luthor leaving Lois dangling off the ledge at the top of a skyscraper in Metropolis while a tidal wave threatens to wipe out a town in Indonesia. What will Superman do? If he can't save both, he has to make a choice, and by necessity that choice will involve a foregone option.
But guess what? In the comics, he manages to do both, to save Lois and the Indonesians. Because he's Superman. He does the impossible. He doesn't let the situation (or Lex Luthor) define his options—Superman defines his own options. He finds a way.
This is most relevant to the end of the movie when Superman kills Zod. After Lois helped the government scientists send the other Kryptonians and their battleship back to the Phantom Zone, Superman faced Zod alone. Zod indiscriminately used his heat vision to reap destruction and murder on Metropolis, and even after Supes had him in a chokehold, the deadly rays from Zod's eyes crept closer and closer to a small group of innocent bystanders. At the last moment, Superman snapped Zod's neck; Zod fell to the ground and Superman fell to his knees in tears.
Superman's remorse was obvious—and so was mine. (Not everyone felt this way; many in the theater cheered, which I've heard was not an uncommon reaction across the country.) This resolution to the story doen't work for me in a number of ways.
First, if Superman had the strength and control to twist Zod's head to snap his neck, why couldn't he turn Zod's head just to divert it from the bystanders? I can let this one go: Zod is a more experienced fighter than Superman is, and perhaps Superman had to put the last of his might into twisting Zod's head without being able to moderate his exertion sufficiently to avoid killing him. Also, this is a young Superman, fighting a physical equal for the first time in his short career. I can excuse him for not having the experience and wisdom to consider other options—people were going to die and he had to make a choice. I get that.
But I don't blame Superman for what he did in the story—I blame those who wrote the story and chose to portray Superman killing his opponent, presumably to make an "edgy" Superman for the 21st century. Even if I accept that Superman had no other choice in that situation, the people who made the movie had a choice whether to put him in that situation. They didn't have to show Superman killing someone—they chose to. They didn't even wait until the third movie, after his heroic ideals had been established and then his "necessary" compromise takes on more weight. No, they chose to show Superman killing someone in his first movie, thereby setting up his moral code for the rest of this appearances in this cycle of films. (Watch out, Luthor.)
And I find that choice despicable. I know full well that tough decisions sometimes have to be made, and Superman is not immune to them. And I love stories that show that moral struggle. But I also love to see Superman find a way to rise above the moral struggle, to show us that if you try hard enough, think the situation through, and refuse to compromise, you can find a way out.
This won't always work for normal human beings, but Superman isn't a normal human being. Superman is an ideal. The ideal. He shows us the best of what we can be. As Mark Waid said on Twitter, Superman shouldn't be written to more like us—he should be written so we want to be more like him. But this is not how the Man of Steel was written, and that's why it fails as a Superman movie.
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I saw Man of Steel Friday afternoon, and Saturday morning I went to Barnes & Noble with my son, who loves superheroes. We always look at both the regular graphic novel section and the rack in the kids' section with superhero books. (And we might happen to pass the philosophy shelves in between, just to make sure all my books are facing outwards. I'm a helper.) There's a new book in the kids' section titled Man of Steel: Superman Saves Smallville
that tells a simpler version of the story in the movie, including the climactic ending. But it tells the ending a little differently:

So there were other ways to end the story without Superman killing his enemy—whew, and here I thought it was just me. (Ironically, the one reviewer so far at Amazon says even this book is too violent for small children!) Sure, in the storybook the villain got away. But that's one of the ways superhero movies usually end: either the villain is captured, gets away, or dies by his own hand (as the hero tries to save him, of course). More to the point, that's how Superman movies should end.
Of course, we can easily imagine situations in which Superman would have no choice but to kill his enemy, and skilled creators could craft an engaging story around it. (See my chapter from Superman and Philosophy for one example.) But an argument can be made that not only would it be a bad Superman story, but that it would not be a Superman story at all. Superman isn't the guy who usually does the right thing—Superman is the guy who does the right thing by definition. Any less and it just isn't Superman.
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Epilogue: I couldn't find anywhere to mention this, but I was also disturbed by the scene in which Clark lets his father walk into the path of the tornado to save the family dog and help people get to safety. I get that it was supposed to show Clark the folly of hiding his abilities at the cost of innocent lives. But it threatens to introduce an "Uncle Ben" aspect to the Superman mythos in which Clark would forever be plagued by the knowledge that his father died because he stood back. Furthermore, it made no sense in story: Clark could have done exactly what Jonathan did (rescue the dog and help people to safety) without revealing his powers, and in the process protecting his father. As shown, it was a confounding story element that introduces an unnecessary and possibly disturbing element to the Superman backstory—another disappointing choice on the part of the filmmakers.