After modest amounts of research, here is how I am currently categorizing the homeless problem. This should be taken as a snapshot of my thoughts, not information for people who have actually thought about this:
1. People who would be fine if there was enough housing
These people have incomes, or would if they had stable housing. The incomes are enough to pay the actual costs of living, but not the rationing-via-price caused by housing shortages. The solution is changing zoning to allow more housing.
2. People experiencing an emergency who can’t afford a hotel
This could be a job loss, or a fire, or moving to a new city ahead of a job. These people need either money for a hotel, or emergency shelter. I think this is the group best served by the current homeless system, and they’re served unevenly at best.
3. People experiencing domestic violence emergencies in particular
Which can be further subdivided into “adults experiencing…” and “children experiencing…”. Basically none of my research has covered this group and I don’t know how their needs differ beyond the obvious, so I don’t have more to say here.
4. People who can’t survive the modern world without assistance
Specifically, the kind of assistance money can’t buy. This covers a wide range. On one end, Julia Wise has talked about certain prisoners she worked with who did fine in the military or in prison, where someone else provided structure to their day, but got overwhelmed by decisions in the regular world. These people might do really well in a halfway house that found them jobs and woke them up on time every morning. On the other you have the severely mentally ill who need multiple full-time caregivers in order to survive. People can be in this category temporarily (e.g. addicts who get clean, or mentally ill people who get properly medicated) or permanently.
We do not have a good system for handling people like this and also respecting people’s rights.
5. The Ruiners
These people can be in any of the previous four categories, or just this one. These are people who impose costs on anyone near them or trying to help them. These are the people who steal from other people in shelters, scream at social workers, and smear feces over public bathrooms. They make provisioning services to the first four groups harder, because they either require you to gatekeep, or allow them in and let them ruin things for everyone else.
Gatekeeping is really costly. It creates friction to seeking help, at a time when people are already exhausted. It puts the staff in an adversarial position to applicants, which will seep into other areas (in fact I think one of the most damaging thing ruiners do is destroy the morale of the people trying to help).
I don’t have a solution to ruiners that isn’t prison, or “pay several people to follow them around and clean up their shit and stop them from threatening people with axes“. In that way you could view them as a special set of group 4- people whose mental abilities are such that they can’t function in society unassisted.