It's hard to envision anyone celebrating the shooting death of a doctor. Or, for that matter, a hospital administrator, a pharma employee, an average U.S. politician or voter. 

But Luigi Mangione's alleged act has revealed a wellspring of hatred for one specific actor among many in the U.S. health system: insurance companies.

How else to explain the 126,000 people posting laughing emojis on a Facebook page devoted to mourning U.S. health insurance exec Brian Thompson, who was shot to death on a Manhattan sidewalk last week. Meanwhile thousands more posted messages online praising his alleged killer.

Mangione, the alleged shooter, reportedly left a brief manifesto declaring that the greed of the health system is amply chronicled in works by filmmaker Michael Moore and Elisabeth Rosenthal, a trained physician and 22-year health reporter for The New York Times.

If you actually read Rosenthal's book, one unmistakable takeaway is that myriad actors squeeze patients in myriad ways, pumping up prices, then haggling amongst themselves about how to split the proceeds.

But insurance companies are the most conspicuous actor. When the bill arrives, they're the one rejecting the claim, hunting for excuses, now assisted by artificial intelligence.

WATCH | UnitedHealthcare CEO shot to death in Manhattan: 

U.S. health insurance CEO shot dead in NYC in ‘targeted attack’

Brian Thompson, the CEO of a major American health insurance corporation, was shot and killed on a New York City sidewalk in what police call a ‘brazen, targeted attack.’ His masked killer escaped on an electric Citi Bike and is still at large.

"If this is related to the insurance industry, it was only a matter of time [before] something like this happened. It really was," Rosenthal, who now works for KFF Health News, told a CNN podcast. 

"There's anger at the executives. There's anger when people see, 'Oh, you didn't pay for my $1,000 test, but you're making $10 million a year.' "

This interview took place before news that the alleged shooter's manifesto included her name and Rosenthal later said that the murder was terrible, tragic and inexcusable.

But she also reiterated her ongoing frustration with the system — where 18 per cent of claims are denied by insurers, where 42 per cent of cancer patients exhaust their life savings. 

She cited horror stories she's collected. Like struggling newborn babies getting rejected by insurance companies questioning whether they really needed that fourth night in the neonatal ICU. This, she says, is an example of a computer-assisted rejection.

"The [baby's] first letter in life is a denial letter," she said. "You know a human didn't write that letter." 

So why doesn't the system get reformed?

Well, to some extent it does. Tiny reforms happen all the time. This year alone, 99 laws were enacted at the state level related to health costs: some states excused medical debt from credit reports, or gave tax exemptions for some non-profit care, or made things easier for patients by guaranteeing that one referral allows multiple specialist visits.

But big systemic change? That's another story. 

The last major reform of the health system occurred under Barack Obama. It's a complex system, and there's no sign it'll be updated in any major way with an incoming Republican-controlled Congress and White House.

If anything, health coverage could shrink. Trump and state-level Republican allies have periodically targeted the Medicaid program for the poor.

Americans tend to like their health plans

Here's the inconvenient truth for anyone pursuing big reform: The political math works against it. That, and the truckloads of money in lobbying and party donations from the insurance industry.

It's true that people say they want change. A strong and growing majority of Americans see universal health care that's guaranteed by the government as a laudable goal. 

But that desire for change crashes up against a rampart for the status quo: The majority of Americans are happy with their current health plan. And they vote that way, judging from the results of recent party primaries and general elections, where an overhaul of the health system hasn't been a winning issue.

It bears mentioning that Americans with quality insurance get some of the best health care in the world. Just compare the number of imaging machines per capita. Compared to Canadians, Americans have multiple times more access to CT scanners and MRI machines, and wait times to see a specialist are much shorter.

There's a mountain of public-opinion polling indicating that Americans are pleased with their own plans. While a majority profess to want reform, an even stronger majority — up to 81 per cent — consistently tell pollsters they're happy.  

Just this week, a survey found that Americans were satisfied with their own personal health insurance by a two-to-one margin.

That's the math problem a politician runs into if attempting reform: You risk upsetting that majority.

Just ask Barack Obama. His party suffered the worst loss of seats since 1938, in no small part because his popularity collapsed during the health reforms of 2009-2010.

Or Bernie Sanders. One of the reasons he lost the 2020 presidential nomination was because younger progressives who wanted Medicare for all were outvoted by older voters, who, by the way, already have Medicare.

It's a detail that bears repeating: The most active voting block in the United States, senior citizens, already has health care under the universal public plan for seniors.

In fact, nearly 40 per cent of Americans, overall, have public coverage; seniors have Medicare, poorer Americans have Medicaid, and there are programs for military personnel and veterans. 

WATCH | Support and praise online for man accused in CEO's killing:

Why is Luigi Mangione being glorified on social media? | Canada Tonight

The suspected killer of the UnitedHealthcare CEO, Luigi Mangione has been receiving a startling amount of online praise recently. David Gilbert, a reporter at Wired, discusses what he's seen online and why some might be glorifying Mangione.

Others fall through the cracks. Roughly eight per cent of the country has no insurance at all, a huge improvement from the pre-Obamacare days, when it was double that.

An even larger share have a poor insurance plan, increasing their risk of stressful disputes with insurance companies and medical providers.

Plan B: Incremental reform

"The American people are outraged and they're rising up across our country demanding fundamental change to a broken health-care system. Enough!" Democratic congressman Ro Khanna said in the House of Representatives this week.

"Across our land, there is outrage at national health insurance companies … denying claims." 

He urged three important changes. Requiring private insurers to cover medicines covered in the Medicare program for seniors; capping out-of-pocket costs so people aren't bankrupted by an illness like cancer; and regulating the U.S. of artificial intelligence to deny claims.

But, really, he added: "We need Medicare for all." 

A number of Democrats support that, or a lesser version of that — like letting younger people pay into the Medicare program. In other words, letting people who want socialized medicine choose to pay the taxes required to fund it. 

That's a dream for another day, with Donald Trump just over a month away from gaining control of Washington.

But Trump did flirt with lesser reforms in his first term. He signed an executive order requiring more transparency in how insurance companies set prices, which his successor Joe Biden said he would enforce, although it's not clear he has.

More transparency would help people shop around for insurance plans, Rosenthal said. It would also force companies to compete on a more open playing field.

Companies are not reporting their denial rates because they're not being forced to — despite existing federal law that lets the government demand it, Rosenthal said.

There's some evidence that Thompson's company, UnitedHealthcare Inc., was repeatedly shown to be one of the worst offenders when denying claims, Bloomberg reports.

WATCH | Lawyer who knew family shocked by Mangione's alleged role in shooting: 

This lawyer knew Luigi Mangione's family. He says he's shocked | Canada Tonight

Luigi Nicholas Mangione, 26, was arrested in Pennsylvania Monday and charged with the murder of UnitedHealthcare's CEO Brian Thompson in New York City following a nearly week-long manhunt. Criminal defence lawyer Thomas Maronick Jr. says he knew Mangione's family and was 'shocked' to hear about the Ivy League graduate's alleged role in the killing.

Rosenthal's book suggests other solutions — more regulations to require transparency in pricing; price limits for certain services; and single-payer care for essential services.

In the wake of this shocking crime, she told the podcast that she hopes insurance companies consider changes beyond hiring more security.

Some are reportedly scrubbing executive bios from their websites, and corporate spending on private security has already surged in recent years.

"Is the answer to increase security? Well, maybe," Rosenthal said. 

But maybe, she said, an additional response is to be more thoughtful, more human, to use less automation in treating claims.

In a column for Bloomberg, health writer Lisa Jarvis said almost everyone has a story about being denied coverage. 

These include sadder ones, like some people being brought to tears while on the phone with an insurer; watching family members suffer without care; or feeling one's stomach drop upon opening the mail.

"We're hearing about how companies had beefed up security even before this event," she wrote. "Those are rational changes to protect their employees. We have yet to hear whether they will make any changes to protect their customers' access to care."