Gonna address this first cause that's like the crux of it all. To my mind this kind of gutless-ness is enough to evaluate the marine rank and file as pretty damn terrible people. Like, perhaps this a matter of a cultural difference between Oda and what you may call ethics fostered within current Western society, but this is absolutely enough for a chunk of the fanbase to view marines as a whole as kinda trash.
This is true.
On this paragraph more broadly, I simply don't think we're meant to treat something like Harald's "oh, the marines are overall a force of good" as something totally inscrutable and taken for granted. I don't think he's meant to be totally wrong about this, but I also don't think it fully reflects reality. Harald's opinions on the WG are, let's be fair, somewhat delusional, and the story doesn't forget to make note of that. Just two chapters ago Imu mocked Xebec for it. And while WG isn't exactly the Navy, it's still its most trusty tool, a tool the agenda of which the WG can bend in awful ways at certain moments of "inconvenience".
I think it's more appropriate to consider Harald's platitudes (outside of his pov and within the scope of the story as a whole) as something that would fully fit a Navy that could be, a Navy that someone like Garp (a marine who's exemplary in terms of morality while still being in that kind oh so messy "perhaps-a--bit-too-loyal-of-a-dog" bracket) wants to make possible.