What Galston is doing here is what the American political class reflexively does in the wake of every tragedy: it immediately seeks to exploit the resulting trauma and emotion to justify all-new restrictions on basic liberties (such as the right not to be locked away against one's will in the absence of a crime or a serious threat to others) and all-new government powers. Every traumatic event -- in the immediate, emotionally consuming aftermath -- leads to these sorts of knee-jerk responses.
Mike Konczal offers a different solution than Galston:
The latest research finds that “the mentally ill account for 16 percent of the prison population, or about 350,000 people on a given day; their true numbers may be twice as high….The solution is not merely to improve the woefully inadequate mental health treatment of prisoners. It is “to improve and expand community mental health treatment” on the other side of the prison walls. But how many blue-ribbon panels have already told us that?”