At least where I am in the US, and in the building construction side of things, there is General Liability and there is Errors and Omissions (which you could call Professional Liability). E&O policies are written for companies or sole practitioners. A company policy will require there be licensed professionals -- and they have a responsibility for all work prepared by others under their supervision. A sole practitioner will not be able to get E&O insurance unless they are licensed. So basically they would be bound by the State's Code of Ethics. Someone with just an engineering degree is not bound by a Code, but they also would not be considered qualified to produce construction design drawings that get reviewed for permitting.Correct so far as it goes. But from a professional liability perspective, failure to abide by these ethical codes can be problematic and perhaps costly, regardless of the registration status of the practitioner.
I am not an attorney, but as a long-time company co-owner I've had plenty of exposure to information about liability. And I've also been involved in construction litigation, which confirmed where liability is ultimately assigned, and I've also seen how some States penalize design professionals (and not unlicensed personnel working under the licensed professionals).
Again, my ramblings are more about the legal implications and licensing body requirements, and not about 'what is morally correct.'
With respect to another post above talking about drivers licensed that is not remotely the same thing...