strong pain meds like morphine and diamorphine should be restricted to the decisions of doctors because of their potential to cause extreme dependence and damage.

You recognize that at least certain things should be withheld from self-prescription.
A lot more medicines have the risk of dependence and damage than just morphine. Drugs in many classes, including antidepressants, mood stabilizers, stimulants, steroids, opiates, and more, cause health-threatening dependence. Overuse of even some over-the-counter drugs can kill you.
Most drugs can cause severe side effects in at least a small percentage of users.
It seems unrealistic to expect someone with sever schizophrenia or hypochondria to be able to select the right medication and dosage.
Overuse of antibiotics can breed resistant strains of bacteria that can infect more susceptible hosts, causing much more harm to certain people. In order to be able to medicate the elderly, infants, and people with immune disorders, we need to limit the amount of antibiotics otherwise healthy people use.
 
For the same reason the FDA prevents the grocery store from carrying dangerous food, I think the prescription system prevents us from having to do research and chemical analyses before we go to the pharmacy.
I agree that doctors are not as informed as we would like them to be and that the system is a little too tightly controlled, but surely the whole system isn't "wrong and should only be controlled by insurance companies."
Perhaps prescribing doctors should have pharmaceutical advisers or prescriptions should contain only a diagnosis and your pharmacist should deal with the medication side of things.