What the hell does that even mean? Of course the state has the right to accredit professional bodies who can then accredit professionals. It's not some deterministic whim of the state deciding who can and can't be a "", it's simple quality assurance for people who are employing the services of said professional.
I believe the argument is not that those without certifications cannot be engineers, but that engineering professions are regulated by the state (via certifications) and thus professions that do not require a state licence must not be 'true' engineering.
Libertarians, sheesh!