Parks in Berlin are littered with beer bottles and cigarette butts because smoking and drinking in public are acceptable there. In many US cities you are not allowed to smoke in a public park where children are playing. Some cities banned smoking in all public parks. Drinking outdoors is banned so you don't see many beer bottles.
The problem in SF is different. You can stare into a park in Berlin and see litter. In SF, a park may seem clean but if you stumble upon one hypodermic needle or human faeces, you may not feel like it's so clean anymore.
My neighborhood in Berlin (Mitte) has homeless people hanging around parks and subways stations, but they don't seem to suffer from mental illness at the same rate as the homeless in SF. As far as number of homeless, Mitte vs the Moscone area are comparable.
Coming from Boston or Copenhagen, SF feels like
an extremely dirty and grimy city. So does Berlin.
It reminds of when I lived in Vienna & had a Swiss coworker telling me how bad the transit is in Austria (if you're unfamiliar - transit is amazing in Austria, to the point where you can live in a small alpine village and not need a car. Switzerland just happens to be one of the handful of countries with even better transit).
[1] I haven't visited Miami in a long time but last I went it was far seedier and grimier than SF, despite lots of rain.
Next time walk down Howard until you hit 6th St. Talk a walk up 6th to Market Street. Then take your pick of Eddy or Turk for fecalspotting.
Also, the shit residents experience is usually there in the morning and someone washes it away by noon, so if you're attending conferences during the day, you probably won't see it by the time you get out.
Personally, I would say San Francisco's cleanliness is similar to Paris', but with more overt drug use.
And I would venture a guess that NO parks within anywhere remotely central locations in Berlin are as clean as this one - not just no used needles/broken bottles but not even "pedestrian" litter like thrown packaging or paper. I don't think you would even commonly find cigarette butts on the grass.
Basically don't do anything but sit, eat your lunch, and look at your phone. The amount of staff people there during the daytime is unlike any other park in SF.
I come every couple of years for a conference in downtown SF (Moscone Center) and always stay a whole week (so I can walk around town before/after the conference - usually going north and west towards the shore/golden gate bridge).
I have not throughout the years noticed the supposed infestation of human faeces. I see a lot of homeless people, but not more than, say, Berlin. And I would say the parts of the city I walk through (and especially the parks!) are actually cleaner than Berlin (and Berlin is not that dirty).
Am I just not staying/walking through the really bad parts? Or missing something else? Or does it just take longer exposure to notice?