You have a point. What enforcement mechanism would be used to force people to buy insurance? It seems to me if the people not buying insurance are so irresponsible, that it would take criminal penalties. When Georgia first made auto insurance mandatory, the fine for not having insurance was $50. That turned out to be no penalty at all. What Georgia does now is to require insurance companies to electronically furnish the state DPS with proof of insurance for the individual prior to that person acquiring state license plates. This is a real pain in the butt for anyone moving to the state, since they generally don’t change their state of residence until after they register their cars.
I think perhaps states could nudge people into buying medical insurance if they hit uninsured with a tax that would be higher than the insurance would cost. This wouldn’t get everyone self-insured, but it would make some headway with semi-responsible people who don’t currently have medical insurance, but would show up at the emergency room if they were sick or injured.