NEW YORK: The protesters started gathering in the early afternoon. Everyone knew they were coming. The sidewalks around Lincoln Center were thick with police, who kept the protesters cordoned off behind riot fences, away from the main plaza and the arches of the Metropolitan Opera. The protesters had microphones, and dozens of wheelchairs, because they were protesting an opera about a man in a wheelchair who was killed, John Adams’s “The Death of Klinghoffer,” which was having its first performance at the Metropolitan Opera, 23 years after it was written.