Charlie Martin is exactly right, and lays it out in clear language. Health Insurance ain’t health insurance.
It’s exactly the same situation as if we charge a 25-year-old the same amount for a year’s term life insurance as we charge his 75-year-old grandfather: it may make the insurance more affordable for Granddad, but it does so by overcharging young Elmo. Add in the “mandate,” so Elmo can’t opt out, and we have a universal care plan that forces Elmo to pay for services he doesn’t get so that Granddad can pay less for the services he gets. But it’s “voluntary” — you get to pick your insurance plan to some extent — and it’s not “tax-supported” because you are just paying the insurance company directly.
And Megan McArdle points out why it’s wrong to force people to pay for something to “protect them from themselves“.
We force everyone to pay into fire departments because fires have very bad negative externalities: if your house catches on fire, unless you live on a rural farm, there’s a good chance that your neighbor’s house will burn down too. Fire prevention is a genuine public good; most health care, with the exception of things meant to stop the spread of infectious disease, simply isn’t.
(A commenter at her site points out that even forcing payments to fire departments isn’t historically necessary.)