Exactly, now you're getting it. Certainly all people jailed for personal possession of any kind of drug and all small scale dealers should be pardoned and dealt with by social workers instead, or simply allowed to live their lives unharassed.
Another thought comes to mind (which I mention just for novelty's sake): even if a full rational analysis says that taking, say, heroin is a bad idea (for pretty much anyone who plans to live for more than a year, or whatever), it seems legalization should open the door to people tweaking the formula to come up with something with similar positive effects and fewer drawbacks. It seems to me that a great way to get people to stop taking dangerous drugs is to make something that's just better and is also less dangerous.
I've read a few things over the years saying that medical and psychiatric researchers (all but the bravest) have absolutely avoided doing anything remotely connected to the illegal drugs because of fear; given marijuana's use in pain management, and more recent results about psychedelics being possibly useful to treat depression and PTSD, this has probably set back research by years, possibly decades.
There are countries with prescription heroin, safe injecting rooms and addiction support not just looking at mental health, but also housing, work and relationships.
There are indications that this strategy works in decreasing harm, decreasing economic impact, and decreasing supply by drying up demand in illegal supply chains.
As always with public health and challenges to existing socio-cultural norms, there’s a lot of room to further discuss.
Diamorphine is already very safe, has few side effects, and is commonly used as a stronger version of morphine in cancer treatment.
What is diamorphine? Well, it's the scientific name for heroin. However, it differs from the drug in being far purer, being used in a clinical setting, and with carefully controlled dosages. Other than that, it's identical to heroin.
This means we can conclude that the negative aspects of heroin come from impurities, addiction, mental health issues of the users, unsafe injection practices, and unknown strengths resulting in overdose.
You can, with access to medical grade heroin, use it occasionally with no negative side effects. We know this because it is used daily in hospitals around the world.
Please read up on the crack epidemic in America in the 1980s and 1990s. You probably didn't live through it so see what widespread drug use does to society and especially cities.