Wasn't he living at home?
Even if not, the situation certainly puts parenting before 18 in question. Not that a parent could do anything about such a deranged minded kid, but it is a question that needs investigating.
Yes, he was. Everything we know about Loughner so far indicates he likely is schizophrenic. It is an incurable disease that afflicts young people, and begins to manifest symptoms in the late teens and early 20's. In the early stages, the parents might easily have thought they were dealing with typical teenage rebellion. By the time they realized his problems went deeper, almost certainly after he turned 18, there was nothing they could legally do. Our mental health system in this country was gutted long ago (by Democrats), and we have no way to commit the mentally ill. We can't force them to get treatment or to take meds. It's why so many wander our streets as homeless people.
Unless it comes out that the parents were abusive or neglectful, it's as much of a mistake to blame the parents for something like this as it is to blame conservatives.