Here is a suggestion that I don't think was covered, though it is risky.
You can write everything from his point of view, including how to correctly perceive the world. When a person develops as a character for the better, this sometimes involves a slow revelation concerning the error of their ways. You can attempt to construct the narrative such that these revelations are experienced by the reader as much as by the character.
People with character flaws usually don't recognize them as flaws. They believe it is justified. If they are arrogant, it's because they truly believe that their capabilities surpass those of others', enough to make the arrogance warranted. If they are cold, it's because they truly see no pragmatic value in giving others kind regard. If they have a dogmatic hatred towards members of an enemy state, it's because they truly believe that this state is so sinister that people who do not renounce their membership of it are necessarily irredeemable.
Write the world from the MC's point of view. Write it by describing it in such a way that:
The MC truly is significantly better than others in the most important traits
The incentive structure for treating others nicely is not sufficient to warrant being kind
The enemy state is so evil that the only explanation for someone being a willful member is malicious intent
The reader should be as indoctrinated as the MC, based on your description of the world. Then, slowly, throughout the narrative, reveal things that contradict this perspective. Hopefully, it should cause as much cognitive dissonance in the reader as it does in the main character. And they would share the MC's revelations that his way of behaving was misguided. Yet, throughout the whole process, they will have sympathized with the MC.
I say this is risky because the reader might perceive this style as you, the author, sanctioning the MC's behavior early in the book.