When a non-Swiss person talks about "the Swiss heroing/drug experiment", they are referring specifically to the HAT program, and not to a free-for-drug park.

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.