Actually, this makes me hate Superman a bit...for being a mouthpiece for the writer.
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.
It's a universal bug I have with mainstream hero comics. It's a black/white falacy at the core. Either heroes kill or they don't. And that's BS. Heroes may not intend to kill, but need to accept the responsibility that someday, maybe, they will by accident action or inaction.
Secondly, Superman's argument is more metanarrative then narrative. It's an attempt to get back to simpler times with comics--which I commend, but not at the expense of all that has come from their development.
Further on that second--the actions do not speak to the words metanarraatively. If you want to be jetpowered apes and time travel, BE JETPOWERED APES AND TIME TRAVEL. You can't have your cake and eat it too.