You think a license makes people honest? There are plenty of doctors and lawyers and other licenses and bonded professionals that behave unethically and even criminally. A license doesn't solve this problem. All a license does is attempt to ensure a base level of functional competence. It doesn't ensure honesty one bit.
The license does two things: it gives the individual more of an incentive to be honest (to avoid revocation) and it gives them leverage against pressures from management. If an engineer can say "I'm not doing that, and if you try to make me, the state board will hear about it and you won't have any (legally mandated) engineers to approve your designs" there is a lot better change they'll get people to back down. It won't stop a dishonest engineer, but it can help an honest engineer who is in a tight spot.