Licensing can help, but only if it is done in the right way.
Remember, legislators don’t know anything about anything except how to get themselves re-elected. When the constituants complain about stuff, like bad construction, the legislators see that they have to act in order to get re-elected. It makes no difference that whenever governement gets involved the situation is usually made worse.
People, in large part, think that their problems can be solved by the government. This is false, but it makes them feel better (and allows them to pass their own responsibility onto others) to believe this.
If contractors (electricians, carpenters, plumbers, etc) are required to meet certain education and experience requirements and are tested (both by a paper exam and a practical exam) before they can get licensed, and are required to take continuing education, that can be a good thing. At least in means that there is some minimum level of verified experience and knowledge involved.
The same applies to HIs.
In Illinois, only roofers and plumbers are state licensed (BTW: To even sit for the exam, plumbers must belong to the union. Go figure.)
Electricians, carpenters, masons, HVAC techs and general contractors are usually required (by some local municipalities and/or counties) to be licensed, but the testing is not always regirous and there is no CE requirement.
Case in point. I know alot about electrical, but I also know that there is a great deal I do not know. Yet, I am a licensed electrical contractor. Sat for the test (open book) and paid my fee. But I would never consider myself qualified to wire a house. I have never worked as an electrician (except for some repairs I made to some of my own buildings) and would not feel right charging anyone to do electrical work for them.
But, according to most municipalities in Illinois (not Chicago. There you have to be union) I am legally qualified to do residential electrical work.
Go figure.
But, I would say that the contractors should be required to be licensed (with the above requirements) before HIs are. This is just plain common sense.
But then, state legislators have never been known for their common sense 
Just my 2 cents.