A lot of people compare Luffy and Smoker’s relationship to Roger and Garp. The pirate and the marine duking it out. Enemies but low key allies in some ways.
With Smoker, he was the hero who saved Alabasta and took down the Shichibukai Crocodile. The government covered up the Straw Hats achievements to boost the reputation of the Marines and undermine pirates. Smoker ended up with a promotion and was extremely unhappy with the result. If we look at Garp, what if the same happened or a similar variation?
What if the Rocks Pirates were defeated with mostly the help of the Roger Pirates but was covered up making Garp the Hero of the story? We know Rayleigh and Crocus aren’t bad dudes whatsoever. Maybe the Rocks Pirates were up to some dastardly things and the young Roger crew got involved. Garp was there and helped out probably.
The Marines didn’t like Roger destroying the balance of Government/Pirates to they made a plan. Cover up the story, make Garp the Hero with a promotion (that he possibly denied), demonize Roger as the “Pirate King”, change his name to remove the reference of the D, and replace him as the force of balance. Maybe that’s why Roger and Garp have respect for each other like Luffy and Smoker.
Seems likely that this would bring about more respect then just them always duking it out. But if Garp truly did it then that’s ok too. I thought this would be very cool though.
*Theory by Babyswagmonster