Case in point: Smedley Butler.

He was a retired Marine Corps Major General, started out as a true believer but paid attention to all the shit he was involved in and eventually realized that he was just violently enforcing the wishes of the wealthy true rulers of the American state.

So when some of them approached him to join the Business Plot, where they'd coup the US government in a similar fashion to Mussolini's Italian coup (basically march a bunch of soldiers and supporters in to the captial while the government is unprepared to defend against a mob and demand the government be handed over, though in Italy's case it helped that they had a system where a monarch held power over the rest of the government and ended up getting their way by promising to leave the king alone). Butler instead sat in meetings to gather information and then turned on them, at which point the government had some harsh words for the plotters (that included GW Bush's grandfather) before sending them on their way to think about what they did wrong (and how to do it more effectively the next time).

This guy wasn't just a marine but a leader of marines and though he didn't question his orders (that we know of anyways) in the moment, he did reflect on everything he had seen and done and didn't like it. IMO former believers who turn are even more important as allies than those who were always on the right side because the ones who have been on both sides have more experience and knowledge about the specifics of how the other side operates.