1) What are you talking to me about? Luffy didn't even know what an alliance was, and is still being silly asking law if he was going to betray him.
2) It's not a development, Luffy has always been like this from the start (Nami, Robin, ...)
3) Luffy has always wanted to protect his friends even if it means keeping them away from the enemy, it's not the first time he's done it
4) This is to be the only time Oda really showed a development of his main character, otherwise it's still the same and even like that 30 chapters later he becomes stupid and "screw up" the infiltration