This is about Dragon mostly, why he wants to destroy specifically the Celestial Dragons. Not Marines.
Okay, so there are many theories existing about Monkey D. Dragon and his past, him being a Marine or Cipher Pol Agent. This theory is more to maybe look at it in a different way. Maybe his time with CP or as a Marine wasn’t what caused him to revolt.
Well first off I do not think that Dragon is a Marine, just because no one really was aware of his existence in the past Reverie when in Alabasta saga we had that mini Reverie flashback:
By Wapol’s reaction, Dragon was unknown, and they don’t treat him as the same level of threat if an Admiral or Vice Admiral was to drop out of the Marines. Like how jaw dropping it was when Aokiji dropped out.
And not like X-Drake who was a former Rear-Admiral that Kizaru knew a lot about.
So how come a rear admiral is known well but someone of Dragon’s power, who obviously would be more powerful than a rear admiral (at least he had to be at that high of a rank in order to gain the knowledge to be able to revolt against the Celestial Dragons). So most likely from this deduction then Dragon wasn’t a marine..
But there’s also the idea he was a former Cipher Pol Agent. Which has even more knowledge than Marines since he works as an assassin (wears mysterious robes and is able to approach silently behind people)
I won’t deny the theories that say Dragon might be a former CP agent and after seeing the darkness of the Celestial Dragons and World Government he decided he can’t stay and must destroy them, since it’s logical, and points to that. But I think there might be an alternate route. No CP agent has ever “dropped out” they are all trained to turn the other eye to the darkness of World Government and Celestial Dragons and to fight dirty as assassins. How come Dragon was the only one to simply not turn the other cheek? We know that they take kids and raise them to know only this style of life, like they did with CP9. They are brainwashed at that age, so how come Dragon was able to not be brainwashed?
What if Dragon is revolting specifically against the Celestial Dragons because of his heritage?
We all know Dragon is a “D.” just like Luffy, Roger, Garp, Law, Ace, Blackbeard and co.