You are Never Alone (when libertarianism is stupid)In the aftermath of a car crash, we can see where the worlds of medicine and driving meet. The other similarity isn't quite so obvious.
The United States has a lot of mental energy wrapped up in the idea of individual liberty. Each of us wants to be in control of our own lives, and don't want someone else to tell us how to live. They are our lives, our choices, and we can each individually deal with the consequences.
Here's some quick examples:
In each of these examples, it's pretty easy to find those who say these should all be individual choices. If someone doesn't make a good coverage a priority in their finances, then that's their choice . If someone decides to not wear a seatbelt, then they'll be the ones hurt in a crash.
And these libertarian arguments - while not very empathetic - are absolutely accurate if and only if driving and health choices are activities done in isolation, with no impacts outside the individual.
It doesn't take much thought to realize that practically never happens. We drive on the roads with other people. If I'm careless, I'm not only risking myself, but everyone else on the road. We live and work around other people. If I'm more susceptible to diseases, I become infected more easily and put other people nearby at risk of being sick as well. And that's without considering insurance  - which is supposed to be a mechanism for spreading that risk out among a group of people. 
Both driving and caring for our health are public activies with public, shared consequences. Treating them as individual, private matters is denying the basic observable reality of our society and world.
 Yes, I am well aware that for many, that is a choice between health coverage and basic needs. That's a separate point.
 Saving part of your income to pay for medical costs doesn't do you a lot of good if you get sick early in your life.
 If my co-worker is riskier with thier health, it may end up making my premiums go up. Again, a separate point.