Your dentist is right. All implants are doomed to fail. I too wanted a zirconia implant. The dentist that performed my cavitation surgery basically finds with the cavitat scanner the bone around implants is almost always toxic to some degree. Regular dentists never see this because the x-ray is generally clear, and they have no other tools to check the health of the bone around the implant. A real shame.
I don't have a problem as such with people wanting implants. The problem is informed consent. If people knew they may have serious health implications they may not want them.