A quack to me is a fake, someone with no credentials. A "gravy train" biller implies to me someone padding charges. Both of those things are different from someone who upsells procedures, which is not unethical and certainly not illegal.
You also stated dentists have no credentialing or general standards of practice, which again is absolutely false if you are speaking of the US. I have no idea where you got that information.
Of course there are some bad eggs but no more than in any other profession. And stating that anyone can become a dentist is just silly. It takes eight years of