That's true, however they also have a tattletale system where everyone's required to report people badmouthing the regime or anything like that. Suggesting anything of the sort to anyone is a huge risk. (Plus whenever someone gets sent to a camp, IIRC their family gets sent, too.)
but then that's just hearsay.
I'd hope a totalitarian regime, however tyrannical, isn't stupid enough to arrest their top generals in a game of he-said-she-said. Plausible deniability still exists unless there's a hard recording of the evidence.
NK's top generals probably understand that NK's position right now is perilously close to a war that they would inevitably lose, and lose quickly. A coup d'etat seems to be the preferable alternative to being bombed into submission and then charged for crimes against humanity for being part of a regime which enslaves tens of thousands of people, arrests political dissenters, and publicly executes people for petty crimes, among other atrocities.
I guarantee you that the generals know that fatboy is as incompetent as he seems.