By that logic, no one is responsible fro their actions, as long as they are acting to punish a criminal and they announced it ahead of time.
In fact, we are responsible for our actions, and their consequences. Enacting justice just happens to be an action that is moral, and has a moral consequence: a “state of justice”. If you wish to decide whether your island idea would deliver justice, you need to look carefully at what its consequences are, and whether you desire them. The reason why I support the existence of prisons, in principle, is because I support what happens in them (in principle): criminals are justly punished. That’s what “taking responsibility for those consequences” means. Do you support and consider justice what happens on your island? (I’d say it’ barely possible to imagine what would happen)
The justice I care about is the justice offered up to those who do not violate rights, I really don’t care what the criminal considers just. Government’s function is to protect rights from those who would deny them. My method is more effective in doing that as it eliminates the possibility of release and repeat offences.
My method also leaves no question just what sort of choice is being made by the criminal or what the consequences are. No one is going to hold their hand and try to rehabilitate them, and prison wouldn’t be being locked up 23.5 hours of the day where boredom is the only hardship. They wouldn’t be fed and clothed and given every other thing they need, like cable TV and movie night it would be hell, and in my opinion it ought to be.
I’d also make sure that people outside knew exactly what sort of hell waited for them if they decided to violate another persons rights.
Is it a brutal solution? Yes, but not for the people who are relying on the government to protect them and those are the people that matter.