Why? Why should the state assume the burden of protecting someone from themselves?
I might see it differently if knowledgeable, well-researched care were difficult to find... but it's not. If someone decides they want to go to a homeopath to treat their terminal illness, why should we stop them?
Consider the costs of seatbelt enforcement. They are real and exist. More, for most people and most rides, the seatbelt truly did nothing for you. To the point that if you got a ticket, it almost certainly cost you more than you are projected to save from having a seatbelt in the short term.
However, for society at large, we tremendously benefit by having everyone use seatbelts. From less time lost on the job, to fewer ER trips from lower collision wrecks.