Consider this. The insurance companies have a clear reason to want to control healthcare - making profit. They have no other interest at all and will maximize their situation with any means possible to accomplish that primary and singular goal. The companies see this not only as desirable, but legally it is their duty - such is the definition of a corporation - and that model has served the markets relatively well for most areas of society where there is healthy competition between the players. Right now however what is driving the healthcare industry is not healthcare issues per se, but the pressures of Wall St demand for ever increasing profit margins. There is no regulation of that.
On the other hand, what dark motives would a government run healthcare system have? What would motivate a government to provide bad healthcare? Governments have checks and balances, corporations do not.
Consider too that countries that have universal healthcare run by governments have better or equal healthcare results than the US while also spending far less of their GDP and the primary reason for that saving is the elimination of the for profit insurance industry. Finally, ask yourself what real service insurance companies add to the healthcare equation. To me they appear to add an approximate and needless 20% overhead. Medicare works pretty well, why not just extend it to everyone and be done with it? Then we can focus on working the wrinkles like cheats and over-payments out of that single comprehensive system.
A transition period of say 10 years could be implemented aimed at reducing the impact of insurance companies employee job loss and share holder movement, where a mixed system of private and public insurance were both offered on an opt-in/op-out basis. (Its clear that altering the structure of 1/6 of the economy is a big task and will require some accomodations).
Then of course, there's the ethical dimension: why should something as basic and critical to the well being of all citizens be made a commodity to be traded on an open market and subject to the vagaries of that market? Why should anyone profit from the life or death situations of others? Why add the expense of life boats to the fares of people who have taught themselves to swim?