I very much disagree. When I didn't have medical insurance, doctors charged me twice what they charged the insurance companies. Insurance companies have a vested interest in reducing the costs of medical care, while doctors have a vested interest in increasing them. Screwing patients out of payments is not an aligned business model, but it only becomes worse when you don't have someone there fighting to reduce costs on your behalf, willing and knowledgeable enough to know when a medical test is superfluous, or over-priced.
Doctors are still prescribing name-brand drugs when equivalent generics are available. That's some really basic stuff that we're still struggling with. Forget it when a doctor asks for a test that you don't even know enough about to say what it does, let alone if you're getting fleeced for money. Insurance companies get to be the bad guy in the middle who both doctors and patients can blame for not paying for things the patient shouldn't have to pay for in the first place.
But remove that stop-gap and you're relying on the blind trust of the doctor to do the work of appropriately minimizing costs for patients in the face business pressure to do otherwise. And if there's anything I know about human nature, is that we're capable of doing what's best for us, while honestly and truly thinking that isn't the true motivation. I've had mechanics try to sell me on nonsense that more knowledgeable friends of mine recognized as a scam. You don't want that when it comes to what is already one of the biggest expenses in a person's life.