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.
@graywolf @anlomedad
In the same way, jailing / sentencing someone for being threatening, and confining them while they plot to murder someone, are two very different aims and comes from two very different worldviews and views about human beings