It's not strictly true that they do no harm to society. A lot of deeply addicted people are still objectively a blight on their surroundings, even if you view it as a health issue that calls for help rather than a moral issue that calls for punishment.
Let's not underplay that damage drugs and addicts do. They're not the source of the problem, they shouldn't be the focus of the solution but let's be honest.
Drugs aren't magical life-ruiners, that suddenly descend on unsuspecting healthy people and destroy them. The people you're describing are mostly already damaged by their own lives, hurting badly, and unable to emotionally function on their own. If you removed heroin or meth from the equation, they'd get drunk, instead... And they'd be roughly the same blight on their surroundings, regardless of their choice of substance.
Our drug problems are, at root, a mental health issue. And neither will ever be resolved in a society that doesn't understand that both problems are one.
Just to add - much of the damage of Heroin, and other drugs cut with fentanyl is precisely BECAUSE it is illegal.
Heroin is smuggled in from Colombia in some mule's intestines and then injected DIRECTLY into the user's bloodstream. This causes many different kinds of fatal blood clots and bacterial infections.
When Heroin was legal in this country (given as a cough medicine to young kids in the 1920s) it didn't lead to a reduction in the life expectancy of the users.
If you are saying addicts commit crimes e.g. burglary well then prosecute them for those crimes, that’s the only way I can take the “blight on their surroundings. Taken a different way, there are a lot of humans in the us who use other drugs, alcohol e.g. who are not considered a blight on their surroundings. Street drugs could be like those drug, and in fact during prohibition alcohol was an illegal “street” drug.
Let's not underplay that damage drugs and addicts do. They're not the source of the problem, they shouldn't be the focus of the solution but let's be honest.