I hear your point but I don't think it's all that effective in a country where horses are not considered *neglected* so long as food and water are made available to them (even a flake or two of weedy hay, and water with larvae in it). That is how it works in my state. No one is going to be up in arms that you are having your horse's teeth floated by *just* a vet.
I don't see how it is such a horrible thing for a state to require an "equine dentist" to have EITHER IAED certification OR a veterinary license to practice. I'm not sure who is getting short-changed here in your argument....nor am I understanding your unconstitutional issue...who is having their rights taken away?