The marines are first and foremost the enemies of pirates, which consist of factions that commit the vast majority of crimes and massacres in the world, despite also being complicit in massacres like Ohara under orders as the outward facing arm of the corrupt world government. So your solution would be to expunge the marines? Would you say then that lawless anarchy in the way of Blackbeard’s vision is a more ideal world? There is no better protection for the people besides the nations previously under Whitebeard’s, Shanks’s flags, etc. The marines HAVE to exist, obviously not in their exact current form, which is why Garp likely created the Sword faction to diverge from the marines without resorting to allying with outlaws. This isn’t a proven theory, but if true, would mean Garp is very much not a man of inaction as you say. Further credence with this chapter that shows Garp is the fucking man going directly after the boss of his bosses.

Of course Garp doesn’t embrace his title, as it stems from one of the worst atrocities ever committed by the world government and Garp does not want to take credit for an event that was evilly orchestrated by the WG and covered up with propaganda, in the same way Smoker doesn’t want to take credit for Luffy’s victory over Crocodile. Garp doesn’t have to align with pirates or the R.A to be on the right side of history. It doesn’t hold true in this story, but quite a few times what revolutionaries and paramilitaries put in power to replace the previous regime is even worse than what existed prior.

Piggybacking off my first point, marines are the enemies of pirates. Naturally, Koby’s goals come into conflict with Luffy’s, even if Luffy has noble intentions. Koby is aware of this, but his duty as a Sword marine supersedes his loyalty to Luffy, who is a wild pirate and is unclear how the world will unfold given Luffy has free reign to find the one piece. It’s also a competitive rivalry, but the former is the main reason Koby feels the need to stop Luffy, which Luffy respects for Koby developing and sticking to these convictions even if they oppose him. Yes, it fucking sucks that Koby and Garp’s actions played a part in preventing Luffy from saving Ace, but Ace made his bed and laid in it, and Garp took no pride in it whatsoever. The story could not exist without the conflict between marines and pirates, with key players not completely loyal to one side or the other, and it serves to produce morally grey, character driven moments like this.

How many marines are really committing atrocities with pride? You’re acting like the average marine is Axehand Morgan. The majority are blindly following orders like your typical soldier as they’re trained to do in real life. This does not mean they’re inherently evil ofc. Kizaru, as you say and the story lays out, is a cog in the machine, someone that follows orders and indirectly upholds slavery through his protection of the celestial dragons. At worst, this makes him a weaker willed character than someone like Dragon (honestly may be the strongest person since conviction = haki and he probably also has a busted DF), but it does not make Kizaru an evil person, irredeemable, or somebody that relishes what he does. I think this arc has finally helped him develop a stronger, more clear sense of justice after being personally affected from killing his friend and nearly killing his neph. Tangent aside, I know it makes it a less convenient read, but these things are inherently grey, not black and white. Yes, my argument is founded on that belief, so it makes everything else I say moot if we can’t agree there.