Exactly, Scott,
We police ourselves, at least those that want to live long, productive lives do. Anyone can dive. If one can purloin the gear, get some air and get to a dive site, he or she can dive. . . no laws against it, other the those of natural selection.
However, once certified, one should endeavor to progress. The progression of which I speak is not only of depth of dives, but also of education and experience.
I'm not the poster child or spokesman for any certifying agency, but it behooves one to learn from the experiences and knowledge of others. That method has been working for a long, long time and I feel certain that it will continue to do so.
Use common sense! Unfortunately that one particular characteristic seems to be falling in the realms of extinction more and more nowadays.
Dive safely.