I just realized I fully forgot to post my extended notes on executions and imprisonment in the One Piece universe? Aha. Whoops. This is a very long post, so I'm putting it under a cut.
While working on Cry Havoc, I spent a lot of time thinking about Impel Down and the judicial system of One Piece because, frankly, they didn't make sense to me. Impel Down is a very large and very crowded prison, which would by its nature require a lot of personnel and a lot of money. The question I kept coming back to was: Why does Impel Down exist? Why is it worth using all those resources to keep it running? Bluntly, why not just execute all the pirates and call it a day?
I did research into the IRL history of executions, especially of pirates, and nothing came up that I felt was relevant to One Piece. The executions of both Ace and Roger demonstrate that people are fine with executions in concept, so no one's arguing against it on a moral level, and I couldn't think of any reason why it would benefit the government to keep captured pirates alive.
Eventually, I started thinking about the executions we do see in canon, and more precisely about the fact that we really only see two notable executions. Which are, of course, Ace's and Roger's. This got me thinking about the well-documented aftermath of Roger's execution. A significant portion of the pirates we meet in canon-- hell, most of the rookie pirates-- have set out to find the One Piece and become king of the pirates. By publicizing the execution and allowing people to hear Roger's last words, the WG allows him motivate an untold number of people to take to the seas. It would make sense, following such a blunder, that they then stop publicly executing people for fear of creating another Roger. Can't make a martyr if you're not killing people, after all.
And I really like this headcanon! I used it in Cry Havoc! I think it's an interesting lens through which to view the events of canon and offers a compelling explanation for the problem I was trying to solve-- and there's canon evidence against it.
Namely, Shiki, who is incarcerated before Roger and not executed, which kind of blows a hole in my theory that not executing people is a new thing. I had entirely forgotten about Shiki, due to not watching the films. He really only gets a throwaway mention in the main series. (I actually texted my friend while I was watching One Piece the first time to ask if I was missing something important, because they mention Shiki so briefly and then never bring him up in canon again.)
So, alright. My tidy headcanon now has a Shiki-sized hole in it (much like Marineford), and we're back to the problem of why he's not executed. The Doylist answer is, of course, that Oda likes to keep his characters alive in case they'll be useful later, but I'm a fic writer and I need Watsonian explanations. For plot reasons.
It is at this point, seething with irritation (especially since I'd already used that bit about Roger in Cry Havoc and I wasn't going back to change it, the implications are FAR too interesting), that I go back to some old AtLA fic for fun and an element of that canon jumps out to me: the big bads won't kill the Avatar once they capture him, because if they do, he'll just be reborn elsewhere.
And I sat back and said Holy Shit Devil Fruits.
Because the exact same logic applies to One Piece. If you kill someone who's eaten a Devil Fruit, the Fruit goes back into circulation and-- given how many pirates have or seek out Devil Fruits-- the Marines have a very good reason to control how many (and which) Devil Fruits are available. If they capture someone with a Devil Fruit, it actually makes a lot of sense that they wouldn't want to kill them. There's no guarantee the WG would be the ones to find the Fruit next, after all.
So that's a really good potential explanation! Now here's everything wrong with it.
I feel like the main problem is obvious: they really don't seem to be trying to keep people alive in Impel Down. Actually, they actively seem to be trying to kill people in Impel Down. Which-- okay, tangent, why not just execute them in the first place then. Why waste the time and money and manpower to make your goddamn hell prison if you're just going to torture people to death. It's logistically illogical.
What was I talking about.
RIGHT. The high mortality rate in Impel Down is the biggest argument against the Devil Fruit explanation. You'd think if they were imprisoning people to prevent Devil Fruits from being used by pirates or returning to circulation, they'd want to keep their prisoners alive. I think you could explain this as being disconnect between policy and people: the guards might know they're supposed to keep people alive, but that doesn't mean they care.
Another argument against it, though, is that there are definitely prisoners in Impel Down who don't have Devil Fruits. In canon, the guards and presumably the higher ups who put him there don't know that Buggy has a Devil Fruit, and it seems like many of the other prisoners on Level One actually don't have Devil Fruits. So what are they doing here?
Honestly, taking the Devil Fruit and post-Roger explanations together might offer the best explanation for Impel Down, but I'm still not quite satisfied. I'm unwilling to simply accept that this is some sort of cultural or ethical situation because a prison like that would be so unbelievably expensive to maintain. I'm also not going to call it a plot hole, because it's not my job to say that things are wrong. My job is to say why things might be right. I'm a fanfiction writer, not cinemasins, dammit. This feels kind of like a zero-sum post. I've come to no good conclusions. But I've been thinking about this for... fuck, fully three months now. I need to get it out of my head or it will consume me.
