[PeterisP]

Being "willing to cross a line" by itself is not mental illness.

A huge part of our crimes are things that are hurtful to society and unfair, but completely natural for dominant primates to do to other primates in their group - i.e., take their stuff for own benefit, or violently attack a competitor. Doing evil stuff is evil, but most evil stuff isn't mentally abnormal, and isn't really curable.

Also, crimes such as 'stealing to feed your family' do cross the line, but are neither sign of mental ilness or even evil. Sure, it hurts others as well - but it is a completely sane decision to prioritize suffering of you and your family over wealth of others; if there is a lack of proper social support and a real necessity, a mentally normal person can easily be stealing 365 days a year.