It really depends on a place. I used public toilets in Europe without much issue.

All of the public toilets I used as a tourist in Europe cost a euro, bathroom operators have an incentive to keep their bathrooms clean. San Francisco (lived there for 4 years) does not adequately maintain their toilets, echoing other comments in this thread, they're literally the worst I've seen. Even the NYC MTA (i.e. subway) bathrooms were better, bathrooms which tend to be portrayed as being especially dirty

All the more reason to not dismiss them as for "people with nowhere else to go" and simply make sure that they are well maintained and people aren't using them as their personal poop graffiti space.