Every homeless person on the street has a story, and every single one of them is a person. I for one would like to know more stories of them. It's easy to condemn all of them saying they're lazy and on the streets out of their own will, but I think every single one of them has their own reason why they're there... and sometimes they've got no other choice.
Old friend of mine used to work as a security guard at subways&trains, and told me a few of those stories. He met many homeless people while working. Some of them used to be wealthy business owners during the 80's, until the economy collapsed. They ended up penniless, and due to some glitches in the system/bureaucracy, had no other choice than live on the streets. After a couple of years of no official address, no jobs, there really isn't any chance of getting a job either - no one wants to hire you. Before saying 'homeless are terrible', keep in mind, that some day it could be you. No matter how well off you're at this moment..
Have to also add, that in my opinion the homeless people I've come across in Japan are generally friendly/pay no attention to other people. No shouting, begging for money or violent behaviour, like with the homeless I've met in various other countries..