By BILL KELLER

ON the subject of the Affordable Care Act — Obamacare, to reclaim the name critics have made into a slur — a number of fallacies seem to be congealing into accepted wisdom. Much of this is the result of unrelenting Republican propaganda and right-wing punditry, but it has gone largely unchallenged by gun-shy Democrats. The result is that voters are confronted with slogans and side issues — “It’s a tax!” “No, it’s a penalty!” — rather than a reality-based discussion. Let’s unpack a few of the most persistent myths.

OBAMACARE IS A JOB-KILLER. The House Republican majority was at it again last week, staging the 33rd theatrical vote to roll back the Affordable Care Act. And once again the cliché of the day was “job-killer.” After years of trying out various alarmist falsehoods the Republicans have found one that seems, judging from the polls, to have connected with the fears of voters.

Some of the job-killer scare stories are based on a deliberate misreading of a Congressional Budget Office report that estimated the law would “reduce the amount of labor used in the economy” by about 800,000 jobs. Sounds like a job-killer, right? Not if you read what the C.B.O. actually wrote. While some low-wage jobs might be lost, the C.B.O. number mainly refers to workers who — being no longer so dependent on employers for their health-care safety net — may choose to retire earlier or work part time. Those jobs would then be open for others who need them.

The impartial truth squad FactCheck.org has debunked the job-killer claim so many times that in its latest update you can hear a groan of weary frustration: words like “whopper” and “bogus” and “hooey.” The job-killer claim is also discredited by the experience under the Massachusetts law on which Obamacare was modeled.

Ultimately the Affordable Care Act could be a tonic for the economy. It aims to slow the raging growth of health care costs by, among other things, using the government’s Medicare leverage to move doctors away from exorbitant fee-for-service medicine, with its incentive to pile on unnecessary procedures. Two veteran health economists, David Cutler of Harvard and Karen Davis, president of the Commonwealth Fund, have calculated that over the first decade of Obamacare total spending on health care, in part by employers, will be half a trillion dollars lower than under the status quo.

OBAMACARE IS A FEDERAL TAKEOVER OF HEALTH INSURANCE. Let’s be blunt. The word for that is “lie.” The main thing the law does is deliver 30 million new customers to the private insurance industry. Indeed, a significant portion of the unhappiness with Obamacare comes from liberals who believe it is not nearly federal enough: that the menu of insurance choices should have included a robust public option, or that Medicare should have been expanded into a form of universal coverage.

Under the law, to be sure, insurance will be governed by new regulations, and supported by new subsidies. This is not the law Ayn Rand would have written. But the share of health care spending that comes from the federal government is expected to rise only modestly, to nearly 50 percent in 2021, and much of that is due not to Obamacare but to baby boomers joining Medicare.

This is a “federal takeover” only in the crazy world where Barack Obama is a “socialist.”

THE UNFETTERED MARKETPLACE IS A BETTER SOLUTION. To the extent there is a profound difference of principle anywhere in this debate, it lies here. Conservatives contend that if you give consumers a voucher or a tax credit and set them loose in the marketplace they will do a better job than government at finding the services — schools, retirement portfolios, or in this case health insurance policies — that fit their needs.

I’m a pretty devout capitalist, and I see that in some cases individual responsibility helps contain wasteful spending on health care. If you have to share the cost of that extra M.R.I. or elective surgery, you’ll think hard about whether you really need it. But I’m deeply suspicious of the claim that a health care system dominated by powerful vested interests and mystifying in its complexity can be tamed by consumers who are strapped for time, often poor, sometimes uneducated, confused and afraid.

“Ten percent of the population accounts for 60 percent of the health outlays,” said Davis. “They are the very sick, and they are not really in a position to make cost-conscious choices.”

LEAVE IT TO THE STATES. THEY’LL FIX IT. The Republican alternative to Obamacare consists in large part of letting each state do its own thing. Presumably the best ideas will go viral.

States do have a long history of pioneering new ideas, sometimes enlightened (Oregon’s vote-by-mail comes to mind) and sometimes less benign (see Florida’s loopy gun laws). Obamacare actually underwrites pilot programs to reduce costs, and gives states freedom — some would argue too much freedom — in designing insurance-buying exchanges. But the best ideas don’t spread spontaneously. Some states are too poor to adopt worthwhile reforms. Some are intransigent, or held captive by lobbies.

You’ve heard a lot about the Massachusetts law. You may not have heard about the seven other states that passed laws requiring insurers to offer coverage to all. They were dismal failures because they failed to mandate that everyone, including the young and healthy, buy in. Massachusetts — fairly progressive, relatively affluent, with an abundance of health providers — included a mandate and became the successful exception. To expand that program beyond Massachusetts required … Barack Obama.

OBAMACARE IS A LOSER. RUN AGAINST IT, RUN FROM IT, BUT FOR HEAVEN’S SAKE DON’T RUN ON IT. When Mitt Romney signed that Massachusetts law in 2006, the coverage kicked in almost immediately. Robert Blendon, a Harvard expert on health and public opinion, recalls the profusion of heartwarming stories about people who had depended on emergency rooms and charity but now, at last, had a regular relationship with a doctor. Romneycare was instantly popular in the state, and remains so, though it seems to have been disowned by its creator.

Unfortunately, the benefits of Obamacare do not go wide until 2014, so there are not yet testimonials from enthusiastic, family-next-door beneficiaries. This helps explain why the bill has not won more popular affection. (It also explains why the Republicans are so desperate to kill it now, before Americans feel the abundant rewards.)

Blendon believes that because of the delayed benefits and the general economic anxiety, “It will be very hard for the Democrats to move the needle” on the issue this election year.

He may be right, but shame on the Democrats if they don’t try. There’s no reason except cowardice for failing to mount a full-throated defense of the law. It is not perfect, but it is humane, it is (thanks to the Supreme Court) fiscally viable, and it comes with some reasonable hopes of reforming the cockeyed way we pay health care providers.

Even before the law takes full effect, it has a natural constituency, starting with every cancer victim, every H.I.V. sufferer, everyone with a condition that now would keep them from getting affordable coverage. Any family that has passed through the purgatory of cancer — as mine did this year, with decent insurance — can imagine the hell of doing it without insurance.

Against this, Mitt Romney offers some vague free-market principles and one unambiguous promise: to dash the hopes of 30 million uninsured, and add a few million to their ranks by slashing Medicaid.

If the Obama campaign needs a snappy one-liner, it could borrow this one from David Cutler: “Never before in history has a candidate run for president with the idea that too many people have insurance coverage.”