How homeless is homeless? Crashing on a friend's couch? Staying with their mom for a few weeks? Living with eight other people in a building nobody's sure who owns? That 99% doesn't imply they're holding down a mortgage or even leasing an apartment.
1. The Mental Health Systems Act of 1980 that closed all Federal mental health institutions, leaving the community of psychiatrists to wrestle with the tough border cases while still tenuously mingling with the locals: totally dismantling the 1946—P.L. 79-487, the National Mental Health Act.
2. The FDA authorized take-home of SSRI and SNRI medicine in 1981 and 1982 respectively. This also marked the rise of mass-shooting in psychopharmacology profiles of such deceased shooters.
https://www.kff.org/wp-content/uploads/2013/01/7684.pdf
We have come full circle from no psychiatric drugs (1820s) to full anti-psychiatry movement today.
I'm not sure if it's an objective of the "Manhattan Institute" to spin up these institutions for indefinite detention, but I will point out that providing housing universally is definitionally cheaper than institutionalization, which is housing with paid orderlies, guards, service workers, etc. If providing housing is too big-government, eviction protections were seen to curb homelessness during the pandemic. And for these right-wing think-tankers, housing affordability also has an available "market" solution which just requires the loosening of zoning restrictions with little other public investment.