San Francisco’s homeless problem has become so grim that tourists wonder if they’ve just wandered into a seedy neighborhood. Last year, a Reddit user posted that he had “walked past numerous homeless” people who were “screaming and running all over the sidewalk near Twitter HQ.” He asked, “Is this normal or am I in a ‘bad part of town?’” The City by the Bay’s homelessness problem is profound even for California, where as much as 30 percent of the country’s homeless live. Municipal officials estimate that 5,823 such persons live in San Francisco, but health-care workers say the more accurate...