Society still has paid at least for your education, depends on your working power to at least fund your dependents, and at least on some degree of reasonableness from you not to raise everyone's insurance premiums.
There's a line to draw somewhere, but even the most ra-ra-individualist heavily depends on society, and has/should have obligations in turn.
Either pay for my health care or get your nose out of it. If my healthcare is going to be my own private matter, then it should be just that. How insulting.
One problem with this mentality is that reality doesn't really make the ideological distinction between whats private and what isn't, or who pays for what. Healthcare is not an intersubjective field, and so actions have consequences, no matter what you think about them.
Vaccines are a good example of this, herd immunity is needed for many of them to work. Antibiotic stewardship is another, unregulated usage of antibiotics risks breeding superbugs.
More generally, "private" ideas are rarely private. Kids born to idiots practicing alternative medicine often die. This scales to societal effects if you have enough idiots. Even though capitalism makes this very fuzzy, many resources in medicine are in fact finite, meaning that time and money spent on one person might mean that another dies. Sometimes that other person is in another, usually poorer country. COVID vaccine availability illustrated that effect nicely.
Essentially what you are advocating is widespread natural selection, with potential consequences affecting anywhere from small local communities to the entire planet in rare cases (COVID is a good one, look up Trichophyton Indotineae for a recent example). And even if you actually do want that, unless you truly follow through, this also comes a huge amount of waste of very limited resources. That is unless you are willing to go the distance and advocate that unvaccinated kids with pneumonia from a measles infection should just go ahead and die because of their parents or neighbors stupid choices.
If you take Kants approach to ethics, that you should only act on principles that you would want to become a universal law, then the principle of healthcare being a private matter is a bit of a non-starter, at least by most ethical systems.
There's a line to draw somewhere, but even the most ra-ra-individualist heavily depends on society, and has/should have obligations in turn.