But the comparison still makes no sense. The president of the US was voted by normal people and is a respected personality with lots of influence. Pirates are criminals who are feared by the normal people. There are a lot of criminals in the one piece world who work together with merfolk and fishpeople, and it has never helped their reputation, because, as I said, they are criminals.
The only thing helping the fishpeople and merfolk to be accepted by commoners and plebs is Neptune's participation at reverie to get recognition by actual world leaders.
How many people that meet the Straw Hats actually fear them though? Most islands are welcoming to pirates in general, it's become the norm. Water 7 is super casual about it, Sabaody has them all over the place, Dressrosa grants immunity to criminals in the Colosseum. And these are islands with ties to the World Government!
We've seen how Luffy's involvement on Fishman Island has spun a positive perspective on the human race for fishmen. Now it's Jinbe's turn to show humans how kind the fishmen can be - someone who's diplomatic and not violent like Tiger or Arlong. This is shown in Jinbe's coverstory where he mediates between the humans and sea beasts. They threw a party for him and the kids played on him. As Otohime said, "The children are watching." By actually being involved in their lives, Jinbe can make a difference like he and Tiger did for Koala. Neptune's involvement in the Reverie is important as far as politics go, but the average Joe Schmo isn't gonna care about that. He needs to see for himself that fishmen can be trusted.