I don't think that disputing the OPs assertion constituted a rant or was off-topic. I had no interest in taking sides either.
SF has many incredibly good systems for helping the homeless - medical care, varying amounts of temporary shelter (SROs are kind of required in SF, but it's terribly implemented, and doesn't actually give people a place to live, just sleep). But the help for the homeless does not involve giving money, but you need money to pay rent, so your only real option is to remain homeless.
Honestly though, I feel there's so much accumulated cruft it would take decades to deal with homelessness in America. For instance, if you turn around and give money to the homeless tomorrow the first problem you'll hit is there are now a few thousand additional people competing for the already limited housing in SF. The decades of mismanagement of mental health in CA mean that you have a huge population of mentally ill who are homeless and may not have cognitive resources to make use of (or even get) the money. You also have to deal with decades of drug [ab?]use in the long term homeless - simply having access to a home isn't going to resolve that.
Democratic Mayor Art Agnos developed a comprehensive program to deal with the homeless problem back in 1989/90 called "Project Shelter"[1] so yes he very much believed in helping the homeless. Unfortunately the Loma Prieta earthquake strikes. He's defeated in the following Mayoral election by another Democrat, Frank Jordan, who shelved the Agnos plan and created his own task force to try to address the homeless problem. So clearly he believed in helping the homeless as well.
However at that same time you had NIMBYs who were upset about the encampment across from City Hall and it was cleared. And you also have have a Republican Governor, Pete Wilson cutting welfare grants.
And it goes way beyond this - the rapid decline in federal public housing development began under Nixon in the early 1970s[2]. The underfunding of the Napa State Mental Hospital was a state issue.
So yes there have been no great successes racked up by Democratic mayors but the problem far more complex and nuanced to lay at the feet of one particular political party and at only the city level.
And again my original comment was not about left vs right, it was about the OPs assertion that a lack of interest in social welfare programs was a "general American thing."
[1] https://www.nytimes.com/1990/07/19/us/san-francisco-treating...
[2] https://en.wikipedia.org/wiki/Public_housing_in_the_United_S...