As for him not being able to understand; is there any evidence that he's different from humanity in a cognitive sense? He seems to operate much the same. Was Krypton that much better? I would think that it's his childhood that would give him absurd ideas.
The devil (or in this case, possibly angel) is in the details.
First off, there's instinct. Human beings have certain expectations about social behavior that are hardwired into us. You might be able to find isolated societies or subcultures where no one cares about marital infidelity, for example- but it's not
easy; the idea of fidelity in long term relationships as a moral thing is very very common. So is the idea that people have a 'right' to get upset, even violent, about it. We punish a man who kills his wife's lover, but very few people express any difficulty in understanding why he did it. And yet it's not hard to imagine aliens among which this is not true- fidelity isn't taken nearly so seriously, or at least isn't a cause for violent rage.
Kryptonians might have very similar instincts, but still differ in subtle ways. Maybe they're less bloody-minded when it comes to keeping up a conflict: more motivated by fear and less by revenge, when it comes to fighting. So when the enemy's means to make war on you disappear, you as a Kryptonian might actually say "okay, no need to keep trying to fight them now." On the other hand you might be MORE likely to give in to the counsel of your fears and launch a preemptive strike or something.
If this were true, Superman might have a persistent habit of slightly
misguessing and mis-analyzing the outcome of his actions on a political scene. Since there are no living experts in Kryptonian psychology, no one would be able to explain exactly why things kept not working out... quite
like he thought.
And he's not clearly insane or even all that cognitively far from human norms. His ideas seem broadly reasonable. "If we destroy the weapons, people will stop fighting" is an idea many, many humans have expressed. But he can still be a bit surprised by people who keep fighting- as indeed many humans are.
(I just made this up, but you get the idea)
Two, yes, upbringing is a factor. He's not raised to think of certain things, although the longer he spends off the farm, the more you expect to see him grow beyond that.
Superman may be an alien, but he grew up as an Iowa farmboy (which really probably didn't prepare him all that well for the harsher realities of the wider world) but the real sticking point is that he's been a reporter for a global newspaper for... how long exactly in continuity? Less than the 70 years in RL, but long enough to have won a Pulitzer and written a best-selling book. That should have taught him far more about how people think and work.
This is true. Then again, nothing says Superman can't try things which are idealistic and impractical, because in his gut he expects them to work, or wishes them to work, or is willing to accept that they'll be only a partial solution to a problem.