https://www.sfgate.com/bayarea/article/San-Francisco-s-worst-street-corners-for-drug-12198945.php
http://sfist.com/2017/05/31/sfs_homeless_outreach_medical_direc.php
San Francisco has unique and known problems that are causing this situation. First new housing is difficult to get approved, high density housing is impossible to get approved. Second the mild weather and young affluent people make it a great place for the homeless to gather. Also high pay for entry level jobs plus the high cost of housing means there are a lot of homeless in San Francisco that are working.
San Francisco is what happens when you have a city that only allows suburb density for miles around. Add to that all the surrounding areas have the same density restrictions and you have San Francisco. Imagine New York city only allowed five story buildings and you get San Francisco.
h/t marathon