Probably because people earning less than average will want to be in the shared pool, and people earning more than the average will want individual insurance schemes.

A dual system where we chose to have our tax dollars go where we want... why stop at healthcare? If I don't want my tax dollars to go to... say the military? Can I defund the federal flood insurance because I feel we need to disincentivize living on the coast as sea levels raise (and personably live 900' above sea level)?

Having individual discretion over what tax dollars goes to leads to an unmanageable mess for those trying to actually create a budget. Additionally, sometimes a national priority and the hard choices that goes with that means having taxes spent on things that aren't necessarily popular with the entirety of the electorate.

The control over the budget comes (in theory) with voting on a house member who aligns with your goals for the budget. Yes - in theory.

> A dual system where we chose to have our tax dollars go where we want... why stop at healthcare?

I think a bit of differentiation could be good, but I draw a distinction here. You get to choose among choices available to you. So unless "not paying for the military" was an option written into law by congress, you could not select that option. And it would be unlikely to be offered, for many reasons, not the least of which is that everyone benefits from the military just by virtue of living within the borders of the US.

I don't think it should be a menu where each citizen gets to select from a huge range of options. I think for some things that would work, but there are many things too fundamental to let people opt in and out.

I would contend that everyone/society benefits from having the population, as a whole, being healthy.

More people who are able to be productive members of the workforce, better mental health from improved financial security, and less cost from preventative rather than responsive treatment.

That also gets to the heart of the problem - not everyone recognizes the benefits that I've suggested from a more universal healthcare system.

I would also contend, that I don't see the benefits from the level of military spending that we have.

I see healthcare as a special case, though (the rule about exceptions becoming the rule, notwithstanding).

The healthcare system is interwoven with rules and regulations. For instance, we already have tax rules depending on your yearly FSA/HSA contributions, tax deductions based on how much money is spent, and most importantly the Obamacare rule that one must have insurance or suffer penalties. Would another exception break the system?

My main concern here is: what happens if someone who isn't paying for insurance ends up at the hospital?

First of all, does the hospital delay care until they can verify that the patient has insurance? What if it's an emergency?

If the hospital doesn't delay care, and afterwards the patient is found to not have insurance, they'd be billed right? What if they can't pay it, and they default? How does the hospital make up for that loss?

Under the current system, I believe the hospital eats the cost, and adjusts their rates accordingly, so the insured end up footing the bill Anyways. A socialized system formalize this, and distribute that cost across everyone instead of just the people who pay for insurance/healthcare.