dangerously mentally ill criminals with violent histories will murder you with a boombox. Or stab children on public transithttp://www.kcbs.com/pages/5794852.php? or in a bakeryhttp://articles.sfgate.com/2008-03-28/bay-area/17168019_1_san-quentin-state-prison-ill-inmates-hunting-knife or because they don't like your beardhttp://www.yelp.com/topic/san-francisco-s-f-pizzeria-worker-stabbed-to-death
You can't even go out to eat with your girlfriend after enjoying an evening on the town without being viciously murdered by screaming, spittle spewing lunatics.
Stranger murders are quite common these days in San Francisco. I avoid SF like the plague. The violently mentally ill and violent illegal immigrants roam the streets attacking and murdering people and the police and city government look the other way, defend, and repeatedly release criminals who have actually shot at, robbed and stabbed people numerous times.
San Francisco, Canada and parts of Britian are a violent sociopath's dream.