The root cause was mentioned in the linked article:
"At the same time, the city was locking and removing bathrooms to help control the rampant drug and prostitution trade they’d spawned"
As was a more humane solution:
"Today, the tents are gone. There are clusters of newly installed portable toilets open and guarded 24 hours a day. More than 60 new hand-washing stations dot the city."
If removing plastic causes this sort of thing, then something critical has been ignored. It's probably best if the society faces that problem and deals with it.
If formal schooling is needed to educate children, something critical has been ignored. It's probably best if society faces that problem and deals with it.
If medication is needed to keep people healthy, something critical has been ignored. It's probably best if society faces that problem and deals with it.
There are no silver bullets, only bullets. Ignore them at your peril.
Platitudes are cheap.
Examine a statement to see if it's logic bears out before saying that it's impossible to approach safely.
Formal education is helpful in treating the root cause of the problem it's addressing, that of knowledge and skill.
Complaining disposable plastic bags are necessary for sanitation because of a large homeless society doesn't treat the root: Why are so many people homeless? (And yes, that problem is difficult and requires a multi-faceted approach... But plastic bags to pick up human shit isn't the solution.)
b) Restricting internal migration or treating people from certain places preferentially also violates most voters' intuitions about fairness.
If American democracy is to end homelessness, anyone must be able to move to New York/San Francisco and immediately obtain a home there that neither they nor anyone else pays for.
Holding out for this doesn't seem like a good plan.