Health Care - What's the point of a public option?

The Democrat political establishment has its heart set on taking all private health care into a public system. They say their proposal is not for a single-payer plan. But everyone knows that is what they want. They say they just want to add competition with the option of joining the public plan. Or you can keep what you have. Professor Greg Mankiw of Harvard asks one question. The two possible answers show that the current proposal is disingenuous. Greg Mankiw's Blog: What's the point of a public option?:

It seems to me that this passage, like most discussion of the issue, leaves out the answer to the key question: Would the public plan have access to taxpayer funds unavailable to private plans? If the answer is yes, then the public plan would not offer honest competition to private plans. The taxpayer subsidies would tilt the playing field in favor of the public plan. In this case, the whole idea of a public option seems to be a disingenuous route toward a single-payer system, which many on the left favor but recognize is a political nonstarter. If the answer is no, then the public plan would need to stand on its own financially and, in essence, would be a private nonprofit plan. But then what's the point? If advocates of a public plan want to start a nonprofit company offering health insurance on better terms than existing insurance companies, nothing is stopping them from doing so right now. There is free entry into the market for health insurance. If a public plan without taxpayer support would succeed, so would a nonprofit insurance company. The fundamental viability of the enterprise does not depend on whether the employees are called "nonprofit administrators" or "civil servants." The bottom line: If the goal is honest competition in the provision of health insurance, the public option cannot do much good but can potentially do much harm.