Yeah I think this flashback pretty much ruined Garp's character for me, not that I was a big fan to begin with. The whole 'he's trying to change the marines from the inside' also doesn't work for me since Garp literally changes jack shit. Akainu becomes the new fleet admiral anyway, and Coby was still gonna arrest Hancock. New gen marines still believe in the WG propaganda.
Garp prevents Ace from being saved by Marco, just because Ace was prosecuted to be Roger's son, while at the same time blaming Ace, Luffy and Dragon for not being marines and staying in the navy despite Garp himself knows willingly that being in the navy doesn't change jack shit against the celestial dragons, gorosei and imu. Go against them and you will just be put down. Even a mad dog like Akainu is now learning that lesson.
What's even worse for me was what Garp said last chapter saying that if he left the marines who would protect the rank and file. I'm sorry, you mean the same rank and file marines that are being indoctrinated by propaganda to carry out indiscriminate genocides for the Celestial Dragons hunting competitions?
As for the marines protecting civilians against pirates, let's not forget that does not include non WG affiliated nations and nations who are too poor to pay Celestial Gold, they instead become hunting grounds for the Celestial Dragons. Not to mention that a large reason why people turn to piracy in the first place is the unjust system they live in of being forced to pay Celestial Gold and just be fodder for hunting games.
So not only is the WG evil and racist, it's also classist, and discriminately genocidal against the poor. Intentionally or not, Oda has made the WG too cartoonishly evil that there is zero nuance left of it being any good beyond just surface protection against pirates at the cost of unbearable exploitation by the WG. It's a lion protects rabbits against wolves world out there for the average Joe.
Luffy rejected the Celestial Dragons and world government from the beginning, Dragon rebelled after seeing the truth. Garp is the only bum still staying because he likes his medals.