The use of the word "disorder" should be noted. ADHD is a disorder, not a true mental illness, though it's often counted as one. I realize that the same can be said for GAD, following my reasoning, but GAD is very different from ADHD. That said, disorders associated with behavior such as ADHD (or even ADD) tend to predispose persons afflicted by them to behavior that's not socially acceptable or otherwise deemed inappropriate. This is because things like impulsivity, frequent movement, lack of empathy etc. are inherent of those disorders. However, I highly doubt that 70% prisoners suffer from actual mental illnesses. Let's keep in mind that mental illness diagnoses make criminals eligible for lighter sentences. Additionally, allowing people to think that criminals are simply mentally ill allows lawmakers invested in jailing for profit to do so with little to no challenge from the public since they're perceived to be doing the world a favor by locking up the "crazies."