What supports that conclusion? There are lots of services – most actually, even insurance services – that thrive with voluntary participation. And the prices are driven down by lots of different companies competing for those customers.
Arguably that militates against treating it as insurance as opposed to a straight-up single payer system or Singapore style system (http://theweek.com/articles/684952/republicans-should-blow-e...), but it does mean you can't argue from the success of existing insurance markets.
Even now, there are places like https://surgerycenterok.com/ that prove high quality healthcare can be provided at affordable prices (they even list them on their website!).