The latest police shooting to roil Chicago was all too familiar — and not because it fits the poisonous narrative of rampant police racism alleged by Black Lives Matter.Quintonio LeGrier's father called police after locking himself in a bedroom when his son menaced him with a baseball bat. When the police arrived, LaGrier, a 19-year-old with emotional problems, allegedly charged them with the bat. An officer shot him dead, and accidentally killed a neighbor as well.The heart-rending case is, tragically, almost routine. Consider two other recent cases. On Dec. 29, Siolosega Velega-Nuufolau of Santa Nella, California, a 50-year-old woman with mental problems, was shot dead when allegedly charging a sheriff's deputy with a kitchen knife.On Dec. 19, police killed Ruben Jose Herrera, a 26-year-old Los Angeles-area man suffering from bipolar disorder, when he allegedly lunged for an officer's gun in the hospital.For all the attention devoted to police-involved shootings and race, mental illness is the more salient issue. A joint report by the Treatment Advocacy Center and National Sheriffs' Association in 2013 examined cases between 1980 and 2008, and estimated that roughly half involved people with mental illness.A Washington Post analysis of 1,000 fatal police shootings in 2015 puts it at about a quarter.These shootings are another tragic symptom of our contemptible outsourcing of the severely mental ill to law enforcement.The police are our de facto front-line mental-health workers — "armed social workers" in the pungent phrase of one observer — and jails are our de facto psychiatric hospital system.In its analysis of 2015 police shootings, the Post found dozens of cases where the police were called as a means of getting treatment. Shirley Marshall Harrison called the Dallas police when her schizophrenic, bipolar son was out of control.He was shot down while allegedly charging police with a screwdriver. "I didn't call for them to take him to the morgue," she said of the cops. "I called for medical help."It's a poignant lament, but why do the families of the severely mentally ill need to rely on the police for medical assistance? When someone has a heart attack or gets cancer, we don't call the police.The answer is simple. In response to abuses, we emptied out mental institutions, but didn't make adequate provisions for otherwise treating the severely mentally ill, who are often left to suffer their delusions with overwhelmed, often frightened family members, or to rot on the streets or in jails."There are less than 100,000 seriously mentally ill in psychiatric hospitals being cared for by the mental health system," D.J. Jaffe, the executive director of Mental Illness Policy.Org, writes. "But there are 365,000 incarcerated. There are also 770,000 on probation or parole and 165,000 homeless."With the mental-health industry essentially abdicating when it comes to the severely mentally ill who refuse treatment or are too sick to realize they need it, the responsibility of the police is increasingly to serve, protect — and deal with desperately ill, irrational people.In 2013, the Arizona Daily Star reported that police in Tucson received "more calls about mental illness than about burglaries or stolen cars."Yes, police should be better trained in how to try to de-escalate. But there always will be legitimate danger in these incidents — cops can, and do, get killed.The Post analysis "found that about nine in 10 of the mentally troubled people killed by police were armed, usually with guns, but also with knives or other sharp objects."A more rational and humane policy would give families robust treatment options before it gets to the point of calling the cops. This would mean more psychiatric hospital beds and more options for mandated care.Rep. Tim Murphy, R., Pa., has a bill to push the mental-health system in this direction. The alternative is to continue to default to police to cope with out-of-control people, often brandishing weapons, and hope for the best — and brace for the worst.