>Disagree. In the case of sex offenders, there is a real mental health issue involved. Permanent incarceration is legit for them.
I disagree with your disagreement. If they are unable to repay their debt to society (serve their sentence & be released back into society) the only conscionable option is to execute them; for indefinite imprisonment is keeping open the risks that they will escape into society or harm those that guard the prisoners, and at the expense of the law abiding members of society to boot.
Unfortunately for your position, the mental health precedent is already in existence for other mental illnesses. The insane desire to rape a young boy (or girl) has never been held on the same level as deliberate premeditated murder. A legitimate insanity defense, AFAIK, has always been a sufficient argument to avoid the death penalty.