IT WILL BE fifty years ago this June that I graduated from Benjamin Franklin High School in East Harlem, in the company of State Senator Joe Galiber, and any number of prominent New Yorkers. I find myself at this half-century mark thinking:  "How much more difficult a city we have now." And wondering where so much went wrong. We were a city of the same size, about 150,000 more persons then than now. And the city was wonderfully able to respond to opportunity when it came.