Severely ill people like Mr. Lanza fall through the cracks, in part because school counselors are more familiar with anxiety and depression than with psychosis. Hospitalizations for acute onset of schizophrenia have been shortened to the point of absurdity. Insurance companies and families try to get patients out of hospitals as quickly as possible because of the prohibitively high cost of care.

As documented by writers like the law professor Elyn R. Saks, author of the memoir “The Center Cannot Hold: My Journey Through Madness,” medication and treatment work. The vast majority of people with schizophrenia, treated or untreated, are not violent, though they are more likely than others to commit violent crimes. When treated with medication after a rampage, many perpetrators who have shown signs of schizophrenia — including John Lennon’s killer and Ronald Reagan’s would-be assassin — have recognized the heinousness of their actions and expressed deep remorse.

It takes a village to stop a rampage. We need reasonable controls on semiautomatic weapons; criminal penalties for those who sell weapons to people with clear signs of psychosis; greater insurance coverage and capacity at private and public hospitals for lengthier care for patients with schizophrenia; intense public education about how to deal with schizophrenia; greater willingness to seek involuntary commitment of those who pose a threat to themselves or others; and greater incentives for psychiatrists (and other mental health professionals) to treat the disorder, rather than less dangerous conditions.