Beutler explains. Money quote:
If it's just a separate, but unequal insurance plan for people who need a lot of medical care, and won't put downward pressure on premiums in the private market, what's the point? Well, it's possible that without the public option, these same, sick people would be paying yet more still. Additionally, as the insurance exchanges grow to include a broader, healthier segment of the population, the mix of people will be healthier, and the public plan's negotiating power will increase. But it's certainly a weaker animal than it could have been.