One Piece is already a little childish but I get the impression that many people want the series to get even more infantile. They are convinced that every "good" marine will fight on Luffy's side when the final battle takes place. Because the WG is evil so only evil people will support them. This is the thinking process of a child. Those "good" marines are in the navy to tell us that decent people can come to different conclusions about how the world should be. They are not there so they can make Luffy's fight against the WG easy. Lots of pirates are pretty nasty. There are good reasons to want to have a strong navy in place to deal with them. Fujitora is not a secret agent of the Revolutionaries and he is no traitor.
