That's awfully glib. There is medical marijuana in Michigan (a relatively restrictive regime, but still) and we still have pretty big problems with prescription drug abuse and heroin. Never mind that marijuana is at least as available as other illegal drugs. It's probably even easier and cheaper to get than a prescription for opiates.
A lot of these people got hooked on opiates through a prescription from their doctor. These doctors prescribing opiates before trying medical marijuana for pain management are endangering the wellbeing and lives of their patients.