I've always found the whole "not killing/being a Boy Scout makes Superman unique" statement to be a bit misleading, to be honest.
While Superman was certainly the first modern superhero, before long, ALL superheroes featured these traits, not just Superman. And many of them conformed to this standard for the same reasons (the comics code, etc).
Even now, Superman is not the only superhero who have somewhat lofty morals in comics; in fact, that's something that most superheroes arguably have going for them.
I understand that the idea that Superman "inspires us to be better", "he's the best of us" is poetic to people. These concepts are also, if we're being honest, not remotely ideas unique to only Superman. Rather, they are concepts that almost every superhero out there has going for them in one form or another.
And even then, I get it, its something that's been deemed inherent to Superman over the years, but the reality of what's in Superman comics tells a different story. And I'm not just talking about him killing. Superman was created as an example of someone good who used violence when necessary. Thus was born the vigilante superhero. That is, at its base, the core of his concept. But how can he be the "best of us" if he's also an example of the "worst" of us?
As a character, Superman has changed with the rest of comics. When MOST heroes were being portrayed as do-gooders with lofty morals, etc, Superman was too, and he was, at one time, the most popular of them, and arguably may still be.
In more recent decades, when comics started to get darker, more introspective, and more like post-modern literature, and heroes and characters became more flawed, Superman quite naturally followed suit. I don't agree with the idea that somehow he should be "immune" to these changes.
He was never "the only really good guy" in the comics anyway. This just seems to be certain peoples' perception. But its not the reality of his mythology, or in relation to other superhero mythologies.
