Last week Americans were shocked and saddened by another mass killing, this one near a college campus in California. We all feel deep sympathy for the families of the victims. As usual, many people responded to this shooting by calling for new federal gun control laws, including the mental health screening of anyone attempting to purchase a firearm. There are a number of problems with this proposal. Federally-mandated mental health screenings would require storing mental health records in a government database. This obviously raises concerns about patient privacy and doctor-patient confidentiality, as well as the threat of identity theft....