Have you ever been to India? I have, and have also visited the bad part of downtown San Francisco many times. Homelessness in major Indian cities is on a whole different scale - I remember taking a taxi ride through New Delhi at night, on some streets the sidewalks had people lying side by side (packed so tight they were touching other people on both side) for what seemed like miles.

On the other hand they don't seem nearly as mentally unwell as the SF homeless.