I'll tell you guys something important regarding Oda's narratives for his characters.
They all have dispositions. The World Government is a representation of everyone being affected by an inherently wrong ideology.
There is only a handful of people in the story who have both a bad disposition and truly try to find the correct way to resolve it. For example, all of the Straw Hats do this and it involved Luffy helping them every time.
The story is about the dreams of people, and how they try to achieve those dreams. Almost every character except for the Straw Hat's and the pitiable characters they try to save/rescue have behavioural problems or problems with society at large.. and it all ties back to the World Government's ideology being imposed on everyone.
This is why Luffy kills people's dreams instead of the person themself... unless they're like Kaido and they are a real threat to the world that needs to be stopped because Kaido's dream was evil, and he would never change it.
People who have evil dreams and the power to realize it will probably be killed by Luffy. This includes Akainu because he is not changing either.
