Earlier quoted context omitted.
I feel like this should really be something people should lose their license over. By deeming something not medically necessary they are (in my opinion) effectively practicing medicine. If they aren't qualified to practice that specialty, or aren't acting in the patients interest we should really be getting malpractice suits on them and stripping medical licenses.
Legally speaking the health plan employee isn't practicing medicine in that circumstance. The requesting provider is still free to treat the patient, they just won't be reimbursed by the health plan. The requesting provider can do it for free, or the patient can pay cash. I do understand that those aren't realistic options in most cases, I'm just explaining the legal distinction.
The reality is that this is the insurance companies trying to have their cake and eat it too. They actually want to be making a medical decision in denying coverage since it gives them a legitimate reason to do so, but want to avoid any liability if that decision was wrong.