Opiates in a controlled environment such as a hospice or hospital ward has endlessly more merit for pain and supressing suffering, but other than that surely marijuana is far less addictive and far less dangerous to consume/take as a medication.
I don't think its a solid black or white decision and must vary from person to person, which strain of marijuana to which type of opiate used, history of the patient and any other factors to consider!
Either way, as a NON smoker or consumer of marijuana i think it should be indeed made legal worldwide to stop it from being a gateway drug and normal everyday people can buy it from a reputable establishment, rather than shady drug dealers who could put anything in it or expose customers to other more dangerous drugs. Marijuana needs separating and can then be taxed, regulated and controlled with common sense! Denial of its widespread usage and criminalising people is just beyond ridiculous and not working in the year 2017