Don't bury the lede. "Open Drug Scenes" (never heard this phrase before) are merely a symptom of homelessness, a problem that has proven to be simple, if not easy, to solve.
A more general example of this is scarcity mindset where the condition of not having enough of something causes someone to be poor at managing that resource [0].
[0] https://en.wikipedia.org/wiki/Scarcity:_Why_Having_Too_Littl...
I'm sure the cause/effect between homelessness and drug addiction is somewhat more complicated (and two-way; I'm confident that I'd be more likely to be an addict if I were homeless).
I think there is delineation between public drug use and open drug scenes. The latter is concentrated.
For a dealer, a dense community of chronic addicts is a cashcow, a market they can serve with much lower risk vs. catering to suburban teenage parties.
Rich or middle class addicts still have houses to get high in.
In my moderately sized southern city of 200k, we logged/censused 576 homeless a few months ago. Of course these individuals were the ones able to be counted; there's likely more. So roughly a quarter of a percent per captia.
As with most US cities of this size and economic demographic we have a few areas where those without housing tend to congregate. Pains me and I wish I could help more than I do. And from what I have seen in my many decades of living here, these areas are totally devoid of this "open air drug market" characteristic. Not to say transactions don't happen they most certainly do, but that's true of every square foot of any US city, and the people in these places shield their behaviors from public eyes as well as anyone else that procures such things. My city is experiencing a staggering increase in violence this past year at a seemingly disproportionately faster rate than other nearby metro areas if my napkin math holds true and yet none of that violence is noted as occurring at these areas I'm describing. I think that's worth noting too.
The interplay of homelessness, mental health, drug dependency, economic struggle and societal rejection is a very complicated and interwoven problem. It's disappointing to hear that there are individuals who feel so self assured in the sources of these problems when it's evident that the qualities of these problems widely differ from place to place.
Say you're living on the streets, mentally ill or just unhappy due to circumstances. Are drugs, a way to temporarily escape your current pain, going to be more or less tempting?
While open drug scenes are comorbid with housing crises, they are not the same thing. There is also overlap between the strategies for addressing them, but that overlap is not complete.
You give them a home. Then they are no longer homeless.
The fact that this is also demonstrably (in several different jurisdictions now) less costly than either imprisoning them or dealing with the other consequences of a significant homeless population should make it a no-brainer.
But too many people have internalized the idea that no one should ever have anything they haven't "earned", including the basics necessary for survival (food, shelter, clothing, clean water, etc), so there's always angry opposition to this. (Plus, of course, the racism angle, which is fairly significant, if often unspoken.)
Drug addiction and the development of open drug spaces is not just a symptom of homelessness. If you solved housing and it became a human right, you would probably reduce the development of open drug spaces, but it certainly wouldn't be eliminated.
With regard to the mechanism of "compensating for the lease of the part of our living planet they should be entitled by birth", I think any means tested or regulated approach is problematic. Instead provide to them rent checks for the slice of the world society has taken from them, and provided to others for private ownership / exploitation.
Let a market economy sort the development and allocation of resources.
We've already run the real life experiments, as suggested above. No need to try to delve into minds and motivation and life goals and other such nonsense (nonsense not in the sense that it's not true, but nonsense in that it doesn't bring any helpful ideas to the policy decisions that should be made.)
As always happens in HN when you post the legal source of a paper, a helpful commenter has posted a link to a grey-market copy. I suggest you read it, then we can have an informed conversation about what you're claiming here, presuming it doesn't change your mind.