Not necessarily. Otherwise, the UK and China would not be making even such innocent objects as steak knives illegal.
It is more than mental illness--but yes--every one of these mass killings; every one of the shootings and murders in Chicago/LA/Baltimore/wherever; every one of the knifings--every single one--is the end link of a chain (sometimes long, sometimes relatively short)of events/attitudes/discipline/lack of discipline/nature/nurture (or lack thereof)/family (or lack)/mental health/mental illness.
I'm sure other factors come into play also; for example, one person once said, "...[B]ecause iniquity shall abound, the love of many shall wax cold." We don't listen to such foolishness today, as we're much more sophisticated. But perhaps that person had a point. Maybe we're barking up the wrong tree. Or trees.
