John Oliver is fed up with politicians using mental illness as a scapegoat to avoid talking about gun control — even as they do little to address the deplorable state of mental health care in the US.

"If we're going to constantly use mentally ill people to dodge conversations about gun control, then the very least we owe them is a fucking plan," Oliver said on Last Week Tonight on Sunday.

Oliver cited the example of Republican presidential candidate Mike Huckabee, who this past week blamed mental health problems for the Umpqua Community College shooting in Oregon. Huckabee, for all his bluster, actually did an abysmal job with mental health care as governor of Arkansas: The National Alliance on Mental Illness gave his state a D minus for mental health care during his time as governor.

But as Oliver pointed out, Huckabee's example isn't atypical in America: Pretty much every politician talks up mental health care after a mass shooting, even though it gets the causes of gun violence wrong and never seems to lead to significant change in how the US deals with mental health care.

We blame people with mental illnesses for violence — when they're less likely to be violent than the general public

The only time mental health care seems to get significant attention from politicians is after mass shootings.

This is unfair, Oliver noted: "The aftermath of a mass shooting might actually be the worst time to talk about mental health. Because for the record, the vast majority of mentally ill people are nonviolent. And the vast majority of gun violence is committed by non-mentally ill people. In fact, mentally ill people are far likelier to be the victims of violence rather than the perpetrators. So the fact we tend to only discuss mental health in a mass shooting context is deeply misleading."

This is exactly right. As Jonathan Metzl, a mental health expert at Vanderbilt University, told me, while many mass shooters (up to 60 percent) exhibit some kind of psychiatric or psychological symptoms, other factors are much better predictors of gun violence — substance abuse, poverty, history of violence, and, yes, access to guns.

"So mental illness is important, but it becomes a scapegoat," Metzl said. "It becomes the one thing we can all agree on — 'Oh, yeah, it must be crazy people!' — but I feel compelled to resist that narrative because it gets us off the hook from looking at society, culture, laws, and other things that hit closer to home for people."

We don't adequately treat mental health

For all the talk about mental health problems, Oliver noted that people with mental health problems still don't get adequate care in America.

"It's a mess, and always has been," Oliver noted, before ratting off numerous problems with how America deals with mental health care. The country used to put mentally ill people in asylums, but these were often so bad they were known as "snake pits." Then the country shut down these asylums, but never really funded the health centers that were supposed to replace them. And now, we tend to deal with mental health through the criminal justice system: According to a 2014 Al Jazeera report, people with mental illnesses are 10 times as likely to end up in prison or jail than in state-funded psychiatric care.

Part of the problem may be that the nation has no comprehensive plan or policy for mental health, instead dealing with these issues through a patchwork of laws. "Our whole system needs a massive overhaul," Oliver said. "The public safety net for the mentally ill spans Medicaid, which is different across the country; eight federal agencies, who administer 112 different programs that in some way touch on mental health; and the social service agencies in each of the 50 states. It is a clusterfuck."

So if politicians really want to do something about mental health, finding out which ideas work and organizing these policies into a comprehensive plan is a good place to start. If mental health is going to be the country's scapegoat for mass shootings, the very least America can do is give these patients the care they need.

Watch: America's biggest gun problem is the one we don't talk about