HAILED as “America’s greatest mayor” in a 1999 na- tional  survey, Fiorello LaGuardia is a figure of enduring appeal. According to President Franklin Delano Roosevelt, LaGuardia gave Gotham the “most honest and I believe the most efficient municipal government of any city within my recollection.” This oft-repeated sentiment has made LaGuardia’s Depression-era mayoralty a touchstone for proponents of activist government both nationally and locally.  But following his lead would be a mistake.