Let's look at this from a different angle.
Not all "engineering" curricula are the same. The Accreditation Board for Engineering and Technology (ABET) prescribes a minimum curriculum for engineering graduates and most states require that, before licensing, the candidate must have graduated from an ABET accredited program. That sets a baseline for the academic side.
The term "engineer", like it or not, believe it or not, connotes someone who is perceived to be a bit smarter than the average bear. This is what the "public" believes.
The title "Engineer" is intended to convey that this person is someone who has received a rather difficult education and has proved himself/herself to be competent to offer the benefit of the education and experience to the public for the public good. The proof of this competence, in the licensed engineer realm, is the Professional Engineering lioense; the P.E.
Without licensing there is no common proof that the engineers are "apples and apples" by comparison. Further, in the event of a failure, the non-licensed engineer may be sued for damages in civil court and if he loses he loses money. If a licensed engineer designs a failure, he can be sued civilly and he can lose his ability to practice engineering by a loss of his license. Which one has more to loose and which do you think would be more prudent in his design? Please note that prudent doesn't necessarily equate to conservative....there's still plenty of risk and innovation in the ranks of licensed engineers.
This question has been debated for years and will continue to be. I am a firm believer in the licensing process and believe that those who complain about licensing should strive to meet the qualifications and become so. What could it hurt? Why not keep the level of public confidence in engineering at a high level and promote that through the licensing process?