When people see the empty storefronts that have multiplied in San Francisco the past few years, they often blame competition from online vendors for the death of small retailers. Supervisor Aaron Peskin sees another culprit: landlords who intentionally keep their properties vacant until they can extract higher rents from potential tenants. Now he wants to repopulate those storefronts by taxing property owners with consistently empty units. “This is by no means meant to be a revenue generator,” Peskin said Tuesday. “It’s meant to be a behavior changer.” Under Peskin’s proposal, owners of commercial properties in Neighborhood Commercial Districts — areas...