There will always be extremists, but that doesn’t make it their core policy. And also, most extremism is guerilla from the other side, so false flags.
It’s literally impossible for there not to some faction that goes against the norm, that’s just human nature. Doubly so when it’s a well established and common espionage tactic.
It’s not movie niceness, it’s how real life is so most know to ignore it, since it’s likely the enemies doing it anyways. And if not, how is it proved?