Here's one factor that might help explain why the health care law's individual mandate is so unpopular: A full quarter of the population expects to pay the tax for not carrying health care coverage.

That's what the Kaiser Family Foundation finds in its latest poll on the health care law. When the health care law's individual mandate gets described as a "tax" - as the Supreme Court found it to be - rather than a "fine," the number of Americans who expect to pay some sort of penalty more than doubles:

What we know about the individual mandate, however, suggests that significantly fewer Americans will end up paying a fine than those who expect to do so. The Urban Institute gamed out the numbers and estimates about 6 percent of the population - 18.2 million people - "will be required to purchase coverage or pay a penalty."

The rest of the population falls into two categories: They either have insurance coverage, largely through an employer or Medicaid, or fall into one of the categories that is exempt from the requirement (such as those who cannot find affordable coverage that costs less than 8 percent of their income).

Of those 18.2 million people, 10.9 million will be low- to middle-income Americans who are eligible for a health insurance subsidy. That leaves 7.3 million people - 2 percent of the population - who will not receive a subsidy and will be required to purchase coverage.

We also have the Massachusetts experience to look at. There the vast majority of residents have complied with the individual mandate, with 94 percent indicating no tax filings that they carry coverage.

Massachusetts' law, however, was pretty popular and continues to be. Resistance to the Affordable Care Act could lead to lower compliance. But from what we know right now, it's hard to see a situation where a quarter of Americans end up paying a health insurance penalty.