Go back to that mental health issues and substance abuse part for a minute. How much do those elements cause a person to not even have a friend's or family member's couch to sleep on? What are the homeless with those issues willing to contribute to a program that will help them out? Will they be willing to recieve psychiatric treatment in a locked hospital and take psychotropic medicine? Will they stay sober? Will they follow rules and schedule their lives like everyone else? Will they allow others to guide their behavior? If the answer is "No" to any of those questions, they are going to be really, really hard to deal with, for anybody. If anyone wants to be a caretaker for this population, they are going to have to put up with a lot of shit. Crazy and drunk don't care how much you are worried about them.