Review Detail of Tasin_Rahaman_1662 in One Piece: Dragon King

Can anyone tell me how MC's goal changed from becoming strongest to replace WG. I mean MC's background has nothing to do with celestial dragons and there is a reason for hating pirates. I don't get it why he wants to remove WG and don't tell me it's because celestial dragons have few thousands slaves in their home and he wants to save them.