It's obvious that if you put all the junkies of a county in a single park, without even the minimal hygienic measures, you create a mess. That's not laissez-faire, that's a mess, but to their credit at least they tried something different than the cycle "heroin user -> scum to jail or to cemetery". It would happen with anything imaginable: "now all homeless are allowed in the Platzspitz Park and nowhere else", a month later the park is covered with homeless trash to nobody's surprise.
The HAT is a step further (not backward) in decriminalization: you are hooked to heroin, metadone doesn't work. But you are not a criminal, and thus we will take a medical approach.
Absolutely, it's harm minimization for both the addict and for the rest of society.
> It wasn’t until a real crackdown that things got better.
Yes, there was a crackdown, but it’s not like this hadn’t been done numerous times before, both in Switzerland and in other countries, so this hardly could have been the major cause of the permanent improvement (which I think we both agree did indeed occur around that time).
> They tried […] the treatments you mentioned
And THOSE were the new factor, and THAT is what made the difference. The Heroin assisted treatment is still in force (an article a few years ago mentioned that about 1400 addicts in Switzerland are in the program).
https://en.wikipedia.org/wiki/Platzspitz_park
They shut it down in '92, which led to junkies spreading throughout the city, particularly on and around Langstrasse.
It wasn't until a real crackdown that things got better. They tried a few approaches like the treatments you mentioned, but that's very different than the laissez-faire decriminalization experiment that blew up in everyone's face.
There's a good documentary or article about the whole thing I meant to recommend but I can't find it at the moment.