It won't teach the perpetrator not to commit the same crime again. Malice only breeds malice.
If it is deterrence, you're too late as the act has already been done; you may argue that it might stop others from committing it, but since this was a deeply irrational crime reasonable consequences didn't factor into it.
Making the victim feel better? Seeing their attacker hurt may seem cathartic on a visceral level but it won't undo the damage.
Making you feel better? That wouldn't be justice, that'd be sadism.
Torturing criminals to "make them feel the same pain" is a visceral response that brings brief gratification, but it's not a solution to anything.
Thing is, there's no such thing as "where guilt is not in doubt". We have a legal standard of "beyond all reasonable doubt", and still we know for certain that this standard, when applied to its full extent as it gets for death row convicts with all the multiple appeals courts, it still manages to convict a nontrivial number of innocent people.
So the judgment on whatever should happen in case where guilt is really not in doubt must be reserved for omniscient infallible divine beings, as we the people simply are not capable of implementing a process that's able to determine when guilt is not in doubt, as all practical experience shows that we've tried and failed and failed and failed to do so.
There can be standards of proof higher than the current ones for torture. For example, another jury whose instructions are “beyond all doubt.” Both juries would need to come back guilty for the torture. Of course no system is infallible, but there is also off the books torture in the current system.
There is no “one true ethics.” There are different methods of ethical reasoning, such as Categorical Imperative / Veil of Ignorance etc, and different conclusions that different people can make using these techniques. You can’t just say “there’s no ethical way to condone” torture/executions/meat-eating and make yourself infallible.
