Firstly, there is no real garuntee that even with non-lethal methodology that someone, somewhere is not going to die from the actions of a superhero. Literally, Batman might accidently kill someone with a knockout gas pellet that the poor sap had an unexpected allergic reaction to.
Well, no, but that's an entirely different argument altogether. Superman (or rather Morrison) is specifically adressing the issue of superheroes that deliberately execute their villains.
If you want to be jetpowered apes and time travel, BE JETPOWERED APES AND TIME TRAVEL.
That was actually what the story was largely about.
That said, readeriif has a point: I like this little coda when taken purely on its own, but it doesn't actually have any bearing on the storyline that preceeded it.