Again, no one is forced to buy auto insurance, or even own a car. They are free to take the bus, even operate a bike (without insurance even!). Owning a car is voluntary. Owning a body is not. Apples to orange comparison when the authoritarians try to force someone to have health insurance.
Being able to travel freely is a right, operating a motor vehicle on the public roads is not, thus the requirement for insurance that most everyone accepts.
Of course you are not required to own a car. But that is not the comparison.
The comparison is: participating in two different realms, and how your participation affects others in that realm.
One realm is that of operating a motor vehicle. If you want to participate in that realm, you must carry insurance to offset the risk that you will harm others.
The other is the realm of being a citizen of the United States. (Yes, you can opt of being a citizen of the US. Plenty of other countries will take you.) The supreme court has ruled under our current law you must carry health insurance to offset the the risk that you will harm others.
Both cases are the same. It is easy to imagine how you can harm yourself or others while driving a car, and it less easy to imagine it if you are simply participating as a US citizen. But the way our health care system is set up, most notably the fact that you will receive free emergency room care regardless of your ability to pay, and also that starting Jan 1, insurance companies must cover you with all of your pre-existing conditions, you can see that you can harm others (financially) with your health.
For both insurance systems to work, all participants must carry insurance, otherwise the pool of participants is too small to spread the risk throughout all participants, then the insurance system collapses on itself.
My question earlier was that when auto insurance became mandatory, I wonder if there was an outcry like there is now about the health insurance mandate. Obviously everyone sees the necessity of carrying auto insurance, and I think over time, every one will see the necessity of carry health insurance (unless we get to single-payer first).