People only see what they want to see. Thats a fact of humanity. Our perceptions are rarely challenged, unless that perception has a voice. Most homeless people do not have a voice.
For instance, 75 years ago a black person was percieved by the general public to be a nigger, a worthless, jobless drain on the economy. Middle and upper class white people rarely saw any value or reason to help them because thier perceptions were not challenged until the 1950's, when civil liberties began.
Fact of the matter was, most black people in that time could not get a decent paying job because they were black. But then our perception changed because people stood up and gave them a voice.
While I am not saying that homeless = historic perception of color, but the fact is that most homeless people have no hope because you can not get a job if you do not have an address and a telephone, if your clothes are dirty because you can not take them off to launder them and you don't have extra clothes anyways.
Another point.....there have been studies of teenage homeless in Seattle, Washington. It is becoming an increased problem and one that leads to young age prostitution, drug abuse, and in some, suicide. Studies have shown that nearly all of these teenage homeless were raped, sexually abused, or physically abused by thier parents or foster parents. That is how they wound up on the streets. Once you get used to living like that, you don't think there is a better world, because your perception is one of horror. Therefor, you live a life of horror, because that is your normalcy.
It is so easy to judge from the outside looking in, but from the inside, its just the way things are. There is no hope, no future, and no repreive. It is a prison of social perception and income, and not one easily broken.