One isssue is that the authorities can't take a person off the streets just because he's crazy (unless he commits a crime, and even then they usually overlook it). We no longer have involuntary mental hospitals. I've called 311 a few times and they call me back (usually). The individuals have never accepted their offers of help or housing. These are folks living outside, no tent or anything beyond maybe a shopping cart. Then cities have tent villages like in SF, I saw some in Vancouver (which seems to have a real problem as well). If you have a tent, you are "covered" and probably have possessions you wish to retain, most of which would be gone if you accepted a housing offer.
To the extent these folks are "crazy", free housing of whatever type won't be appealing by and large. Crazy includes both mentally deranged as well as drug addled, they don't know where they are basically. This is probably a small percentage of folks in tent villages, but significant for the homeless. The tent thing is not very apparent around here, I see some on occasion when driving, but the next time I come through they are gone, I don't know exactly why.
And of course the notion that at some point these folks will "rise up and burn everything down" is not one I think has much to it, nor is the risk of communism very high in my view. The burning arises usually from some police incident which leads to protests which can degrade into riots and then looting and burning.