Talking about Hitler is boring but maybe it makes sense in this context. Inflicting suffering on Hitler would have absolutely no deterrent effect, but I think the vast majority of people would do it given whatever confluence of magic and time travel made it a possibility. Someone on the level of Hitler or Stalin or Mao deserve the suffering regardless of any deterrent effect it may or may not cause, simply because of the raw amount of suffering they caused.
I don't think it's unreasonable to think that at that level of 99-100/100 evil that can be true, but even just a few steps back and it's not so clear-cut anymore.
> Someone on the level of Hitler or Stalin or Mao deserve the suffering
I think that's the crux here though. You're talking about retribution. Causing them to suffer makes you feel good. It doesn't prevent any further suffering from being caused, it doesn't create a deterrent (not that those work all that well anyway) and it doesn't change their behavior. It just satisfies you by providing sadistic joy as an outlet for your anger at them. This is easier to imagine if you believe in such a thing as "evil people".
Personally I don't think framing people as "evil" is useful or even meaningful. It offers no explanatory power and it provides no mechanism to prevent future harm. Germany treated the Nazis as uniquely evil and ended up enacting very narrow bans on that specific kind of evil without addressing the underlying mentalities, systems and relations that enabled or even encouraged it.
For a fictional example (to move away from Godwin for a moment) consider Harry Potter: the stories reveal various horrifying details about the wizarding world from the casual attitude to chattel slavery of an entire species, to the existence and employment of the Dementors that literally suck all life and joy out of you, to a horrifying prison system, to rampant bigotry against mixed-lineage "mudbloods" and not to mention the entire extended canon surrounding the oppression of goblins; and yet once the Big Evil is defeated, none of these things are challenged and the protagonist decides to become a public servant, helping uphold the system unchanged. Even though The One Who Shall Not Be Named is established to be inherently and undeniably evil, to any careful reader it should be obvious that the entire system is flawed at best and directly harmful at worst yet the hyperfixation on "evilness" as a sliding scale attribute rather than an emergent property denies any challenge to the status quo.
> Inflicting suffering on Hitler would have absolutely no deterrent effect, but I think the vast majority of people would do it given whatever confluence of magic and time travel made it a possibility.
"Kill him painfully" polled at 14.4%. Makes me doubt the vast majority agree with you.
I have a feeling being personally responsible for inflicting said suffering may affect the outcome a bit. I struggle to envision any world I'd be willing to torture anyone. Even Hitler.
I don't think it's unreasonable to think that at that level of 99-100/100 evil that can be true, but even just a few steps back and it's not so clear-cut anymore.