Emphatically, yes, doctors should be able to prescribe whatever they think is best for their patient. But I would agree with Barbara that as an insurer you have a responsibility to determine what you will pay for. I think under a public program that's financed by taxes in a redistributed fashion and that proposes virtually universal coverage, you will run into a problem of unsustainability that will lead you to rely on rationing and central planning exercises, like telling doctors what they can prescribe for patients.
I think a better way to approach this is through a private insurance model and mandatory purchase rule that would achieve better outcomes, including preserving a physician's right to prescribe what they see fit for their patient.