The only reason methadone is used vs. heroin is that is was supposedly harder to make on the street and more addictive allowing it to take over in the addicts mind as the preferred drug. Given that it is harder to make, it ensured that one would have to go to the legal dealer and do the drug in a controlled manner.
I’m of two minds on the methadone side of things…I believe in the legalization of drugs, but I also want to see people cured of addictions if they want to be. Methadone really only shifts the dealer to a physician and ensure pure product. And my time in grad school for psychology tells me that most methadone dealers aren’t interested in curing anyone…they are interested in profits. It was always strange how no one was ready to get off the drug until their insurance ran out and then and only then were they ready to kick the drug (i.e., legally, the clinics cannot stop treatment in the US, but they can decide to ween their nonpaying patient off the drug now that they are ‘ready’).