False. SF is a cesspit in any part of downtown, tenderloin, SOMA, the Mission, and pretty bad in many of the other parts. Every day for the past week I've watched a mountain sized pile of shit slowly grind down (by being kicked, stepped on, and rained on) into nothingness outside of our office. It's quite frankly repellent.
Now that I think of it, one time a (presumably) homeless man took a shit on the wall of our office building. It was there for weeks.
*Further SF horror stories: I've also witnessed a homeless man take a dump on the fence down the street from us in broad daylight. Also a coworker has seen a pile of dump propped up against a neighbor's door, and witnessed the shock of said neighbor as they came home to discover it.