For most New Yorkers, the word “public” is a good thing: public transportation, public libraries, public parks, public sanitation, and, much of the time, public schools and even public welfare and public housing. Not that we don’t have our complaints. Most of us are well aware that the services we depend on are too often diminished and undependable. But very few of us would venture that they should be abolished. Even our billionaire mayor takes the subway.