I bet a substantial faction of the marines will think it's all for the greater good if flooding the entire world would rid them of the pirate nuisance.
Nah yall don’t understand the Marines.
Most Marines (even baby killers like Sengoku) think of themselves as the protectors of the innocent. “Pirates are bad because they kill innocent people, we Marines protect innocents.”
They are willing to overlook shit like Ohara because they believe Ohara keeps the world safe for the vast majority of people.
Once the Gorosei try to sink the whole world, watch even Akainu and Ryokugyu defect. Even Ryokugyu values the “stability” most of the world enjoys thanks to WG discrimination. The WG killing the entire population is not something he will coooperate with.
It may take some time, but the Marines will not aid the Government in the end. There is no way.