@anon178560: Perhaps so, but if they're in jail, at least they're getting three meals a day and medical treatment, as opposed to what happens to them on the streets.
However, Post no. 3 is correct. Most people in jail are criminals. And many are poor. They do not have the money to hire a high-priced attorney to plead them down to a lighter sentence.
It's also a known fact that the majority of long-term homeless people are mentally ill and non-compliant with their medication. Since the reform of the mental health laws that disgorged thousands of mentally ill people on to the streets, with no legal strictures on them to continue their medication, they went off their meds, lost their jobs and subsequently became homeless.
It is sad, but that's the truth.