I love how One Piece fans made up Garp and Sengoku into being "super goody goody marines", when pre-TS it's already established they're willing to stay in the marines acknowledging how fucked up the CD are. This flashback only cementing it.
If you were Sengoku or Garp fan cause you thought they were these super duper good guys, instead of just normal military men with moral standards. You weren't a true fan, sorry to say.
W Oda for cooking with Sengoku this flashback. No horseshitting about it. They, just like Kuzan/Borsalino/Sakazuki/Smoker/Hina/etc, are willing to turn their face to the shit the CD do, while being able to do other good things like fighting criminals and saving civilians at large.
This is also why I've always maintained is Akainu had a direct mentor it was Sengoku.