BILL COSBY'S Wednesday visit to Baltimore did nothing for me but bring back a bad memory, one only a week old. None of this was Cosby's fault, mind you. My experience occurred in Cambridge, Mass., during my three days at a liberal re-education camp. You know it better as the college formerly called Harvard University. OK, so I'm kidding. A little. I spent three days in Cambridge, where members of the Trotter Group, an organization of black columnists, held their annual meeting. There were several symposiums held with liberal cognoscenti in the Charles Hotel and at several places on the...