I agree with JTT. If as he says we are to accept that some helpless psychopaths are driven to kill, and are incurable, then surely they are acting in a way that they have no contol over, due to mental illness.

It is definitely advisable that they be removed from an open society, and their actions be supervised and monitored, so that they can not harm again. But I do not see why their living conditions should be significantly less comfortable than the not mentally ill.
Should we really be punishing the sick?