> If it is a necessity (I think it is), it's not clear to me how it can not be compulsory.

But you wouldn't make that claim of any _other_ vital service, would you? Food, water, transport, medicine ... all these and more are provided by voluntary payment - or by charity for those who can't afford it.

What's special about Government that it requires compulsion to fund?

All those things are funded for at least some subset of the population, and heavily subsidised for the rest, by the Government. Also, I think it's pretty obvious that "voluntary payment" for healthcare didn't work for many, many people, and has resulted in thousands of deaths and significant needless pain and suffering every year.

In that case you are arguing that taxation isn't necessary.