There are a few standard policy objections to the single-payer Medicare for All proposal backed by Bernie Sanders and Elizabeth Warren, who share second place in the ongoing presidential primary behind Joe Biden. Two of the main complaints—that “socialized” medicine insults the American system of providing goods and services through the free market, and that it would mean spending a lot of money—don’t resonate much with Democratic voters, who are OK with the government paying for health care services and with big public spending in general. But a third critique of M4A, as it’s called, has had more potency: that its elimination of private insurance would be disruptive to individuals and families who would be forced off plans they are currently comfortable with.

Polls consistently find that Democrats (and the general public) support a “public option” Medicare expansion that would exist alongside private insurance more than they support a sweeping single-payer plan. And thus debate moderators have repeatedly returned to “Would you eliminate private insurance? WOULD YOU?” as their favorite wedge question, as they did Thursday night in Houston, with Biden and other candidates happy to oblige them by directing fire toward the lefties.

There are a few ways that M4A advocates can respond to the private insurance question. One is to point out that once we decide that universal health coverage is a human right, it doesn’t make sense to keep providing it via profit-seeking middlemen like insurance companies. Another is to point out that private insurance is a pain in the ass that involves doing a lot of paperwork and being hit with a lot of seemingly inexplicable extra charges even after you pay your premium.

Sanders and Warren used a mix of those responses Thursday night. “Every study done shows that Medicare for All is the most cost-effective approach to providing health care to every man, woman, and child in this country,” said Sanders, noting that it would “eliminate all out-of-pocket expenses, all deductibles, all copayments.” Said Warren: “What this is about is making sure that we have the most efficient way possible to pay for health care for everyone in this country. Insurance companies last year sucked $23 billion in profits out of the system. How did they make that money? Every one of those $23 billion was made by an insurance company saying no to your health care coverage.” Sanders mentioned that his M4A bill would eliminate medical bankruptcies, and Warren talked about M4A ensuring that Americans would have access to their previous doctors.

But those last points only hinted at the possibility that the case for single payer could be constructive rather than defensive. Guaranteeing universal coverage for all citizens, eliminating greed-driven inefficiency, and stopping cancer-driven bankruptcies from occurring are, certainly, all compelling reasons to support Medicare for All. Another, though, is providing personal security.

The idea of eliminating private insurance is frightening because the idea of getting a new health plan, in America, is frightening. When people think about being taken off a policy that is currently providing their medical care—however annoying and loophole-laden that policy may be—they’re terrified, because we’ve all been conditioned to understand that the alternative is a paralyzing, vulnerable second-class status. The defining feature of American health care, even beyond the high costs, is the fundamental unpredictability it means for everyone.

This is where Sanders and Warren, who have otherwise educated voters about progressive policies so effectively as to change the parameters of American politics, have fallen short. They haven’t acknowledged that core fear of destabilization during their debate appearances. And so they haven’t made their answer to it—that M4A would mean people would always be covered, for everything—tangible. They haven’t told the narrative of what would happen if you were sick or injured in their vision of single payer: going to a doctor’s office or hospital without having to look up whether it accepts your insurance plan, receiving treatment without having to worry that you’re being subjected to a given procedure just to bill the insurance company for it, and leaving without being charged (then or by mail two months later) for a deductible or copay or enormous surprise out-of-network balance.

Rather than conveying the feeling of security that they’re selling, they’ve treated the private insurance question as one of efficiency and outrage: Under M4A, it would be unnecessary and illogical to keep private insurance around, and getting rid of it would stick it satisfyingly to some bad actors. They haven’t addressed the gut-level worry that the phrase “losing insurance” triggers—and explained that their proposal isn’t “kicking you off” your health coverage as much as it’s kicking everyone onto a plan that you can never lose.