The stench of urine and feces is dominating, the random exposure to homeless folks mental problems is a daily occurrence, drug paraphernalia (eg: heroin needles) and trash are scattered throughout. SF downtown is an absolute dump.
Go ahead, take a 30 minute walk just north of The Mission. Turn a corner and you'll find a homeless dude standing with a vacant look on his face and pants around his ankles, letting his penis sway in the morning sun.
Turn another corner and you'll find someone shooting up with reckless abandon.
Turn another and you'll be an uninvited witness to a homeless dude verbally and physically assaulting someone for no reason.
LA, NYC, Boston, Chicago, Seattle, etc -- at least these have their size to distribute the problem, SF on the other hand is so small and its city council so progressive that there is a critical mass of it all.