I can comment on the part about homelessness, SSI, etc., from personal experience. First SSDI requires you having put a certain amount into the system, so it's not available to everyone. And getting SSI is a lengthy process. What happens if you lose your job and have no money or resources? You're out of luck. You apply for food stamps, SSI, etc... and you get medical and food stamps. The medical might get you to the point where you are diagnosed disabled, supposing that you can be organized and able enough to get to the proper doctors. That's something not always possible, ironically sometimes because of the very disability that causes all the problems to begin with.
Anyway, let's suppose you get the diagnosis from the proper authorities. Then you submit your info to the government and wait for the first rejection to come. After 2-3 years (sometimes longer, almost never shorter) you get that rejection. Then, if you are able, you find a lawyer who specializes in the area and is also ready to take you as a client. "But of course a lawyer will take you," you think, "there's money in it for them." One would assume so, but that's not always the case. Sometimes you get lucky though and a lawyer who rejects you refers you to another lawyer (speaking of which, what address do homeless people use to send and receive all this info? I've never thought of that... ??)
So let's suppose you get a lawyer and you file your appeal. I suppose you could also file an appeal without a lawyer. They don't really do anything special, basically just coach you so that your story sounds plausible but terrible--basically in line with what your medical records indicate, but the worst possible scenario that your records would allow for. Also, if you get nervous or whatever they can help with support there while the judge grills you and expert witness(es) at your hearing try to poke holes in your case. Ok... but the appeal. You appeal and then wait some more time. All told it's going to take years, if you get it at all.
Then you apply for public housing. You might have tried to apply months in advance... but then if you didn't have money for the rent/deposit when they called your number then you'd be screwed and go to the back of the line anyway. And back of the line usually means a waiting list. So more waiting. You might get lucky and get hooked up with some social services that helps you out (e.g. giving you the money required to get a place). You might also be able to get a job after you had become homeless. Of course that's not as easy as some seem to think, especially the longer you're homeless. And the very reason you're homeless might be what prevents you from getting or keeping a job.
Such people, usually with mental rather than physical problems, would be helped by a civilized society to get out of their hole. And there are resources, and it is possible, but it takes time. It also requires the people to help themselves, and that is not always possible... because of the illness. Some people just don't care enough, or for some other reason aren't able to help themselves. A lot of people have no clue what this is like. If someone gets cancer or some other "physical" problem, it is always accepted that they can't do certain things or will have certain issues. On the other hand if it's a "mental" problem, people (even family/friends) usually say something about them needing to "man up" or "want to help themselves" or whatever. Sometimes this is possible, sometimes not. Often it's speaking from ignorance. The same person probably wouldn't say: "Gee, you have diabetes? All you gotta do is tell your body to stop being insulin resistant! Your pancreas probably already is working fine, why don't you just pull yourself up by your bootstraps and conquer this? I don't understand why you need medical help? Just fix it! It's easy!" But this is essentially what many people with mental illness (and some other issues) are told by others.
Does everyone go through the above process? Not necessarily. I didn't. I was only homeless for maybe 5 weeks, I received help from family and the government, and I haven't been there since. However, this is because, while my illness(s) are debilitating, it is not to the extreme that I couldn't get things forced through the correct hoops. I also had family who helped me out for several years make ends meet. If they hadn't helped I would have been on the street. Not everyone is so lucky.
Of course that doesn't mean things are easy either. And most here don't realise the extent of my problems. If I may speak a bit more personally than I have before (in hopes that it gets people to understand the problems people sometimes run into)... people on this forum think I, for one example, change my beliefs every few weeks, or every few months, or maybe twice in one week. Ha. Sometimes I change it multiple times in one day. And every switch--say from Orthodox to agnostic--makes perfect sense to me in that moment. It seems almost a required thing to do, because it just seems like how things have to be. To be what I just was yesterday, well I can think of so many reasons that I can't be that anymore. Until tomorrow, when I switch back again.
And that's not just in religion--as though changing your entire belief system is a small thing anyway. Another area is education. That tends to change several times a week. Some people don't know what they want to do when they get out of school, so they switch majors while in college. I'm almost 33 and I change my major quite often--sometimes just a few times a month, but more often several times a week. In rare instances I change it several times in a day. And when I say I change it, I don't mean on a whim. Again, it makes perfect sense. And often I spend hours and hours reading about these areas of study/employment. I spend hours planning out what I would have to take this semester so as to transfer to another school, so as to set me up best for graduate school, so as to set me up for employment down the road, etc. (and yes, I've also tried to not change, tried to not worry about it, tried to make myself stick to something, tried... a lot of different approaches. Anyway...) It's not uncommon for me to plan 10 years into the future. And then after I'm done, 10 hours in the future, I change my mind. Btw, 2 days ago it was theology. Today it's mesoamerican archaeology. Tomorrow? I dunno. But today's idea of archaeology seems perfectly normal and sensible to me. I have 101 reasons that I can't do theology anymore, and 101 reasons why archaeology makes perfect sense. I've convinced myself that I needed to do something different. Threw away some theology books as well, because I'm not doing that stuff anymore.
And believe me, I don't go through these cycles because I haven't attempted to break out of them. I've tried over and over, all sorts of ways to break out. By the time I was 21 I had dropped out of vo-tech (about 4 months before I graduated) and dropped out of college twice. I had quit 5-6 jobs, usually by not showing up (or simply walking out). When I got married things improved in some ways, because I had a more direct/close/understanding support system. For a while I was even able to hold on to jobs here and there for about a year, though there were still significant issues. When my wife died I grew a lot emotionally, I made a lot of steps forward as a person. However, as far as stability goes I went backwards fairly fast. When she first died, I started back to school like 7 days after she died. I used school as a way of taking my mind off things, and got all As. In the 3 semesters (plus summers) since then I've been a 2.0 student. That's along with a bunch of withdrawals. Doesn't have anything to do with understanding the material, it's all about whether I can stay focused long enough.
Does this sound like a good way to live? Normal? And think about this--in spite of how screwed up I am, I am better off than a lot of people out there. Why are there homeless people? Some just run into some bad breaks having to do with their job, family, etc. It can take quite a while to dig yourself out, withg the length depending on how bad off you are and what resources you have available/are aware of. Other people are truly screwed up and screwed over.
--A few other notes. Regarding welfare, food stamps are supplemental, and do not pay for food for an entire month (unless you're eating Ramen noodles 24/7... and I would guess that some people don't have stove tops or microwaves available to them). Also, medical through the government does not guarantee you can just walk into a doctor and get help. Even if that doctor takes your medical insurance, there is no guarantee the doctor will agree to see you. I know, I've been rejected in that way.
--Sorry if too much personal info above. Life is odd. If you sat down for a drink or dinner with me I would appear perfectly normal, if a bit shy/awkward, unless I told you otherwise. But of course the truth is indeed otherwise.
--I hope I'm not going to regret saying all this
And please for the love of God don't try to give me pointers on how to improve my lot in life. I've been seeing therapists for 16 years, I've got all the "tools" and "coping strategies" an such that I need