From someone in the healthcare business whose judgment and expertise I trust a great deal:

Subject: I’m sorry but that guy AND ramesh are wrong..
Jonah, I think you know my views on this but i will restate. #1) the auto insurance analogy is appropriate – not because people need health services as a result of someone else’s direct negligence but because it is other people’s irresponsibility or low income that force all of us to pay their costs through higher health care prices (due to cost shifts as a result of uncompensated care provided by docs and hospitals,) through higher taxes that pay for government programs (Medicare, Medicaid, public health clinics and hospitals…the list is long) and through higher premiums for our own insurance. folks that don’t have health insurance are still getting health care – but it is paid for by those who pay taxes and who have health insurance. therefore, like the accident victim, we all have an interest in seeing people purchase health insurance—to protect ourselves.
#2) Conservatives wish there was a way to do this without a mandate. the problem is that even when you subsidize the premiums to make them more attractive to the low income (and even middle income these days) studies have found that people still don’t take it up. The government gives away health coverage to low income woman and children (Medicaid, SCHIP), but they still have trouble getting people to sign up for these programs. what usually happens is they have a health need, visit the ER, and the hospital that wants to recoup payment for the service signs them up for assistance. also, without the mandate, many people will only sign up when they get sick – this leads to gaming of the insurance system which raises cost considerably for everyone.

And, a follow up email:

it should also be noted that Romney’s goal was “universal coverage” – if that is your goal (and you could argue whether it should be) then you MUST have some kind of mandate on coverage…either through single payer or through individual purchase mandates. you may recall back in the Hillary Care days, there was a big debate whether we should be pursuing universal coverage vs universal access, the latter meaning we should do things to make insurance more affordable to folks but not require they buy it. again, as i noted below, universal access does not generate the across the board savings and benefits to the health system that a mandate does because people will game the system.