Is Diacetylmorphine (Heroin) really THAT bad?

Opiates have been used for thousands of years for both recreational and medicinal purpose. Heroin is actually still used as a pain killer in Europe, and is 100% interchangeable with morphine other then dosage.

Assuming you were prescribed Heroin by a doctor, why would it be worse then any other opiate?

As a pain patient, I take Oxymorphone daily, which is said to have greater euphoria then any other opiate, including heroin. It is 2x stronger then Oxycodone (Oxycontin) orally, 4x stronger intranasally, and even more stronger then that when IV'ed. I still get dope-sick from my medicine if I wait too long in between doses, and if I was to come off the medication I would have severe withdrawal. In the 1970s, Oxymorphone had to be removed from the market because addicts were specifically trying to get their hands on it even over heroin. In 2006, under the brand name Opana, it was brought back into the pharmaceutical market. Even though I take it as prescribed, I get the best feeling in the world when I take it, a side effect I really dont mind at all.

How is this any different then if I was prescribed Diacetylmorphine in a pill form (such as in Europe)?

I am not including needles, disease, prostitution, and so forth. Strictly speaking in terms of a medication being prescribed by a doctor and its effects when taken correctly.