Why? In short, for all adherents of the "free circulation of hard drugs".
Please read the story of the substance's appearance.
Heroin was once on the free market. naturally, clean, because then it was not prohibited and there was no point in diluting it with anything.
True, it was not with us, because it was not invented with us.
Then in the west the authorities several years later figured out how hard it was to hit society and quickly banned it.
Do you understand? this was the case with any drug.
At first it appears and no one forbids it because it has just appeared.
A year passes, maybe 5 years, sometimes more, and the country starts to react to the drugged citizens , understands that citizens are not able (or a substance such that there is no other way) to use dosed and prohibits such a thing.
This is not the first and not the last case.
Opium, Morphine, heroin, cocaine, LSD, meth and so on, so on, so on. it was all once legal and was banned after.
The country, by and large, does not care how you spend your free time, if then you can go and work normally and also give birth to normal citizens.
Otherwise, it does not restrict you
I think it would be about the same if high-quality potassium cyanide was absolutely legally sold in supermarkets in clearly measured doses - someone bought this product for himself, someone died from its use, most would ignore it, there are many more other good stuff.