I encourage you to lookup up Housing First if you have not already. While it may be misleading to say there are 16 million vacant home to half a million homeless people (32 homes for every homeless person), for the reasons you mentioned, it is entirely possible house these people.
No one who knows about this issue is thinking about warehousing people. Like you said they need a stable place to live, access to services, transportation, and work when they are ready.
Wow, that really put it in perspective. How far we have let greed get the better of ourselves. Where are the guardrails to prevent this?