Listen, I'm not making this crap up for giggles. The law is that boilerplate adhesion contracts are usually unenforceable when it comes to consumers. Yes, contracts between businesses are legally binding, as they considered "sophisticated" parties and have the opportunity to negotiate terms and hire counsel prior to entering the transaction. However, consumers are afforded additional protections when entering into contracts with merchants and service providers.
As for your counterargument that the patient is free to choose amongst many different providers... yes, this is true in some situations. But there are also many instances where this may not be the case, such as in a remote rural town or a highly specialized area of practice. And many people show loyal allegiance to their family doc and would not be willing to change. In any case, service providers are generally viewed as "unique" in the eyes of the law, i.e. getting your tonsils removed by Dr. X is different from having Dr. Y do the deed, even though they are performing the same operation. In essence, you are bargaining for a completely different service if you go to another doctor, since they are not fungible.
Finally, I would think that courts would look with particular disfavor upon a waiver of rights in the area of health care, which is considered a necessity. From a contracts hornbook I have on the shelf (note: adhesion = essentially forced to sign to get the product or service):
"Many kinds of adhesion contracts are unenforceable because they are signed against public policy. A contract requiring an individual who needs an essential public service, such as medical care, to waive any claim for negligence on the part of the provider is likely to be found contrary to public policy and therefore unenforceable." (emphasis added)
I think that sums it up better than I did.