I disagree that it undermines that at all. Some people are able to be rehabilitated, some aren’t.
In addition, rehabilitation, like other complex psychological things like grief, is not a linear nor fully understood thing. Someone exhibiting anti-social behavior may not be able to be rehabilitated at a given time due to many possible factors, be it intrinsic to the individual or collective knowledge. Even if one cannot be safely re-integrated into society, there are ways that they can voluntarily contribute and likely would choose to, even if it were for selfish reasons (ex. many serial killers are aware that there is something profoundly wrong with them and happy to contribute data to prevent others or get their names in books).