Oh, I get where you're not following my position. Sorry, I assumed that was a given.
The public option lowers costs by inserting some honest competition for price into a system that has stopped really bothering trying to keep prices down. The public option has no profit margin, so in order to compete with it the private companies would need to lower prices and be more efficient than the public option in order to make a profit. A public option also has a stronger bargaining position with the providers because it is bigger. A pharmaceutical company can afford to walk away from negotiations rather than take a reasonable price, say with one of the five insurance companies in Indiana, but it could not afford to walk away from the public option like that, so it would need to bargain.
For capitalism to work, what you ideally want is a perfectly informed consumer making rational purchasing decisions based on price and quality. Our health care market doesn't work like that at all. A person has some control over who they work for, but that choice has virtually nothing to do with which health insurance company that employer works with. The employer picks the insurance policy pretty much just based on price and doesn't care about quality. The doctor is who actually decides what products to buy for the patient and he only cares about quality, not price at all. The insurance company only cares about price relative to other insurance companies. If it is paying $1,000 and so is everybody else, it can just jack up rates. All of this is clouded in a thick haze of incomplete information. Nobody actually knows what conditions, of the tens of thousands possible ones, they are going to get some day, or if their insurance will cover what treatments and whatnot. People have no choice other than to go off of this vague "well, I think blue cross is probably good since I've heard of them before" sort of decision model... So, the capitalist mechanism that runs off of informed consumers making rational decisions just doesn't really apply to the health care market. It's too bumfuggled up. The public option fixes that. The government does have the capability to absorb and analyze all that information. Because it is driven by votes, it has an incentive to make rational decisions about both price and quality, and it negotiates directly with the providers. It breaks through the flaws in the market, and by doing so it would force insurance companies to do a better job in order to compete with it.
In an ideal world, we would launch a public option and nobody would sign up for it. It would release rate information and insurance companies would get their act together to beat those rates. It is more important as a way to prod the companies into behaving themselves than as an actual provider. But, if the companies fail, it would be there to catch us.
Also, you talk about it as though it is an entitlement. That is not the case.