Correct me if I'm wrong, but I do believe that many mainstream Democrats (i.e. Robert Gibbs) fail to understand why the 'professional left' remains so angry -- to its very core -- that a public option was not included in the Affordable Care Act.
Here's why: with Medicaid, Medicare, the VA and high-risk pools subsidized by the government, the cost of financing health care for the poor (and generally sicker), the elderly and dying (oh, and also those with super-expensive stuff like end-stage renal failure), veterans (deservingly higher users of health care), and those with major pre-existing conditions is all socialized. In other words, government socializes -- what we can describe using heartless-insurance-industry-speak -- the 'loss' of paying for needy health care users who will most certainly 'take' more from the system then they 'give' through tax dollars. Yes, we could just leave these people to die - as some Republicans want -- but the American social contract, as weak as it is, reflects our collective decision that doing so is morally unacceptable.
So, who is forced -- remember, there's no public option -- to deal with the bureaucrats at Aetna and Cigna? Yup, the people who -- God willing -- will never actually need much health care. (Remember, the majority of health care spending occurs in the last years of life.) That is the middle class, the wealthy, and the healthy. These folks represent tremendous private gains for any health care system -- their contributions are a net positive whether they are sending premium checks to Medicare (in a Medicare-For-All system that most liberals wish we had) or to Aetna or Cigna. The kicker? These folks don't have a choice to be socially-responsible citizens and send their 'net positive' contributions to Medicare, Medicaid or the VA -- no, they are forced (and under ObamaCare, by law) to send their healthy-person premium dollars to Aetna and Cigna, who, when they don't pay out enough dollars in health care get to keep a little bit to send to their CEO's golden parachute account, or to shareholders on Wall Street. In short, private, for-profit corporations get all the goodies from the healthy, instead of those goodies being used to strengthen programs that serve everyone in the most efficient way possible (i.e. Medicaid or Medicare). (And, yes, the ObamaCare medical loss ratio requirements do help make this situation a bit less horrible, but private insurers still get a whopping 15-20% to waste on advertising, fancy buildings and insane CEO salaries).
In a nutshell, the U.S. health care system socializes the 'losses' of insuring the sick, and privatizes the gains of insuring the (relatively -- since nobody will never be completely healthy) healthy.
So, where does the public option enter this story? The Affordable Care Act institutionalizes a system that sucks money -- whether via tax dollars, premiums, or unnecessarily high deductibles and co-pays -- from people of all economic stripes, but particularly the middle class, and subsidizes the gains of private health insurance corporations that do absolutely nothing to actually improve health care in this country.
Liberals want a public option, because consumers should have the choice to be good citizens and send their health care dollars to a program that serves the broader good, rather than just the pockets of plutocrats.