Dang, this chapter just came straight outta nowhere but feels entirely believeable. Oda did a good job setting this up I think. It's an excellent example of how good Oda is at character development. Shittier writers who flanderize their characters, especially Shounen protags, into stereotypes, would never allow their main character to act as Luffy did right here. Allying with a lesser evil so easily against a greater evil, especially when there are other ways to do it that have less moral issues? Never. But Luffy stays in character, and is entirely willing to do exactly that. It's part of why One Piece remains so good, in how good of a grasp Oda has on all of his characters and how well he writes them all.