A number of cities in the United States have begun providing "free" needle exchange programs for drug users, especially among their homeless populations. Generally, it is believed that the sharing of dirty needles has increased the incidence of the HIV virus among drug users.

Are these needle exchange programs really "free?"

What costs are borne by various individuals and groups in these free programs? Why are individuals and groups willing to bear the costs associated with these programs? (What are the benefits?)