The homeless tend to fall into three categories. 1)Situationally homeless due to recent circumstances.  With some support the people in this group move on to better things. 2) The chronically mentally ill.  A rapid increase from policies many years ago which closed long term facilities designed to house and support. 3) This category includes many sociopathic individuals or people who choose to live on the fringe of society.  These are frequently drug abusers and behave in other criminal ways.  They may or may not have an psychiatric disorder depending upon who you speak to.

We may have to just live with #3, but there are services and supports for #1 and #2 although funding is sparse. It is better in the long term to give money, if you are so inclined, to agencies which provide services.