I'm afraid there is no excuse for "patient confidentiality". You're either Fit or Unfit to fly, doesn't matter what the inherent condition is. If a Dr suspected a Pilot of having a terminal illness, the pilot is immediately grounded. That Dr has a duty to report to the employer/authorities that the pilot is Unfit to fly, the issue remaining confidential. Because if the pilot doesn't declare himself unfit they continue flying...
That is true with the AME, although he can only report unfit to fly to the authority. And yes, i had the displeasure to endure that myself and came back to flying (not mental illness though, just a garden variety thing). Any GP cannot do that and in fact is barred from doing that by law. Laws can change, but i do not see it happen, instead i wouldn't be surprised if pilots have to endure a psych evaluation additionally to the normal medical. And of course part MED might change as well, i guess any kind of anxiety disorder or mental illness will lead to a permanent loss of medical in the future which is good for all those guys without a job.