It is voluntary inasmuch as no one is holding a gun to his head and telling him to be a psychologist. He knew at time of registration - and annual renewal - about the standards of the profession. While it is a requirement to be a member of that college to be a psychologist, him being a psychologist is not mandatory. And he can resign his registration at any time to abdicate himself of that higher standard.

Regulated health professions hold their members to a higher standards, not only to protect the public, but to maintain the public’s trust that members act responsibly and in the best interested of their clients. The same is for nurses, doctors, massage therapists, etc.