These are not assumptions, but fact. How can you not know that our annual per capita expenditures on health care are the highest in the world, double those of the most expensive single payer system, and at least triple most of the rest? Of the G-20 countries, all have universal health care. Except one. Us. Despite being ranked #1 in health care costs, we are ranked 30th in outcome, not only behind all 19 of the other G-20 nations, but behind 10 developing nations as well. That's what makes it substandard. NONE OF THOSE NATIONS WHICH HAVE ABANDONED MEDICINE FOR PROFIT HAVE EVER MADE AN ATTEMPT TO GO BACK TO IT (and please don't try to pass off that nonsense about a for-profit system being destroyed forever and unable to come back, as that is just rank bullshit.)
When I entered college in 1969, the high-tech sector of the economy did not exist, but now it is a multi-trillion dollar sector. Whole sectors of the economy can't be destroyed forever, unless replaced by a new sector (like the carriager and buggy sector was replaced by the internal combustion engine and automobile), or regulated, like the patent medicine/snake oil market regulated by the FDA (and the second that regulation ceases, the sleazeballs come roaring back), so the notion that medicine for profit could be destroyed forever is laughable. The profit motive cannot be destroyed. If you don't believe me, ask the Russians or Chinese how their pathetic, deadly experiments in eliminating profit as a motive turned out. Commmunism was and is doomed to failure, as it is based on a precept that flies in the face of reality: "from each according to his abilities, to each according to his needs." What utter and complete bullshit. That is why the "worker's paradise" (spare me) lasted all of 70 brutal years, because you not only can't legislate or regulate the profit motive out of existence, you can't even stomp it out of existence by deadly force. The only thing you can do is to admit to its shortcomings and inadequacies in certain areas of human existence (like healthcare), and egulate it to optimize its overall effect in others.
If your goal is to deliver health care to as many citizens as possible, a for-profit system is the worst system possible, because maximizing profits depends on maximizing revenues and minimizing expenditures. It is inherent in the nature of the for profit insurance system that premiums be jacked up as much as we will allow (maximizing revenues), and coverage will be denied as much as we will allow (miminizing expenditures). The goals of affordable healthcare for as many citizens as possible, and the goals of any for-profit entity are mutually exclusive. Expecting insurance companies to moderate their policies without government intervention is not only unrealistic, but shows a complete misunderstanding of a corporation's fiduciary duties to its stockholders: it is required by law to maximize returns to its investors, so it is illegal for a corporation to voluntarily moderate its revenue increases by holding the line on premiums or voluntarily increase its expenditures by not withholding care from the sick, and anybody who expects otherwise hasn't got a clue.