A dangerous sentiment on the left threatens to derail what could be the biggest progressive achievement in half a century. It’s the view that any health-care reform that doesn’t include a public option isn’t “real” reform and thus isn’t worth doing. This mantra has become an article of faith among many Democrats who haven’t necessarily thought through the matter but who take their cues from leaders advancing this argument. Unless liberals rethink this premise, and fast, Democrats will squander their best chance in a generation to end the scandal of the uninsured, bring health security to every American family, and begin the long-term process of getting national health costs under control.

The first fallacy of the “public option or nothing” mantra is the notion that we’ll never cover everyone without a Medicare-style program for Americans under 65. The experiences of Switzerland and the Netherlands prove that this isn’t the case. Both have pioneered market-based universal health care. Both cover all their citizens using private insurers, and they do so for much less cost — 10 percent of gross domestic product for the Dutch and 12 percent for Switzerland, compared with 17 percent in the United States, where nearly 50 million people are still uninsured. Those countries also boast better health outcomes than we do, even when compared with states with similar demographics, such as Connecticut and Massachusetts.

A related fallacy is that the public option is the most important issue to debate. It’s not. The central progressive breakthrough in any reform should be to make it possible for every American to access group health coverage outside the employment setting — access that does not currently exist but which the proposed insurance exchanges would enable. What’s critical, therefore, is the structure of these exchanges and the rules about who would be eligible to use them.

Liberals should make peace with the notion that a regulated market of competing private health plans can be the vehicle for getting everyone covered. Yes, it means that unlike some other advanced countries, we’ll have billions of “health” dollars siphoned off by middlemen and marketers. But if liberals think of it as a jobs program, they’ll learn to love it. If everyone’s covered and insurer “cherry-picking” is dead, health insurance will come to look more like a regulated utility.

Those on the left still seeking incentive should consider: In 2006, Sen. Ted Kennedy urged Massachusetts Democrats to support Mitt Romney’s plan for universal coverage via a competing system of regulated private insurers, paired with an individual mandate and subsidies for low earners. Kennedy knew this would become a model for a bipartisan fix for the country. Now, a Kennedy-approved model is within reach. Liberals, far from resisting it as a setback, should celebrate it as a triumph.

Matt Miller, a former Clinton White House aide, is a management consultant and the author of The Tyranny of Dead Ideas. A version of this commentary was published by the Washington Post on Tuesday.