It really isn't difficult to imagine becoming homeless, which then leads to depression and other mental issues and then using drugs to escape that. So some proportion of the "problem group" are going to be redeemable too.
For example, I knew a man that was incredibly ornery, almost always drunk, and prone to occasional violent outbursts. Everybody (including the rest of us in the camp) avoided him. About a year after I left the camp, I ran into his daughter and learned that he had been a normal, successful eletrician that had sustained a severe brain injury at work, and his employer managed to avoid paying for workman's compensation or helping with his medical bills, leaving him permanently disabled and with no safety net.
I knew another man that also received a brain injury during a car crash in which he also lost the only extant copy of his masters' thesis in anthropology (the crash occurred in the 80s), and was in a similar position.
I knew a man that actually managed to get a section 8 apartment, but lost it because he opted to move back to the riverbottom and let a pregnant homeless woman stay in it in his stead. He was then also cut off from ALL social programs.
I saw a man get banned for life from an entire network of shelters spanning a huge chunk of the state for taking three (3!) single-use packets of Tide laundry detergent out of the facility.
I have also met a (very) small handful of genuinely odd people that just preferred to live mostly off the grid but still wanted to be near their families/veterinary clinic/spouse's grave/etc. but they are very much the exception and not the rule. I think that for some people with limited experience with the homeless, people that are chronically homeless might appear to all fall into this category.
I do 't think this happens all the time, or even to a majority of the population, but it is an idea that I have heard repeated numerous times.
From my experience, the details are almost always surprising, and the search for simple explanations or solutions is frustratingly unsatisfying.
Homelessness doesn't cause depression, which is a biological illness. Depression, uncontrollable anxiety, addiction, etc. are the root cause of the vast, vast majority of homelessness.
[1] http://www.nationalhomeless.org/factsheets/addiction.pdf [2] http://www.nationalhomeless.org/factsheets/Mental_Illness.pd...