When I moved to SF in 2007, I basically walked around and said to people, "Yeah, I can see why the Sanctuary Districts started here." Of course, nobody had the slightest idea what I was talking about.
But the city does have an enormous homeless problem. A lot of homeless people come there from other cities purely because the weather is better and the parks are huge, so they have a better life as homeless people even if they never intend to, or assume they will never be able to, become non-homeless people.
Either way, Sanctuary Districts are really not the solution to the problem. But sad as it may be, I could definitely see it happening one day.