First of all this question much oversimplifies human beings. There is no such human as you describe it, that is a cartoonish hypothetical. There are ppl who have periods of violent psychosis, sure, and there may be someone who develop a strong psychopathic behavior with homicidal leanings.
You can confine such ppl while they pose an active threat, but you cannot sentence them and forget about them. Their confinement is predicated on the threat being active.
@graywolf @anlomedad
While they are an active threat to others, they can choose to undergo reform as a way to prove that they are no longer an active threat.
The point of saying no to jail, is to emphasize that a person is fundamentally free, and that taking away their freedom must be the last resort and a temporary solution. In cases of active conflict, you can kill someone, but your aim isn't to kill, but to render the opponent incapable of harming, to contain their threat.