Pretty sure if it was an officer of the North Korean military having done the same thing, everyone in the world would be applauding him.
Resigning and speaking as a civilian, or running for political office would be equivalent of silencing yourself in this situation. Nobody would listen to you when your words pose no threat to the establishment or the command chain. Literally the "don't like it, then leave!" attitude.
Too bad for his family, but imho he did the right thing, and if more people like him would step up, things would have some hope for turning for the better.