This is not hard to understand

Jacob Hacker, in Salon:

I think it’s pretty clear why if you look at what’s happened over the last generation in American health insurance. Private insurance plans have basically failed us, and we need to have competition between a new nonprofit public health insurance plan that puts patients first and not private insurance companies.

I’ve argued that the public insurance plan really achieves three critical goals. It serves as a backup for people who want to have a good plan that’s available in all parts of the country and that provides them with a broad choice of providers. It provides a benchmark for the private insurance plans, encouraging them to improve the delivery and cost effectiveness of care and keep their premiums down. And it offers, finally, a cost control backstop because public health insurance in the United States has actually done a better job than private plans of keeping costs down over time, and it could do a much better job in the future if it were given the authority to innovate in the payment for, and delivery of, care.