BÜCHEL, Germany — This pointed insult was shouted without a trace of irony through a chain-link fence toward a group of nuclear weapons opponents last Tuesday by a military guard equipped with binoculars and wearing a camera strapped around his neck. The protest group was at the perimeter of Büchel Air Force Base in west-central Germany on July 12, the 205th anniversary of the birth of Henry David Thoreau — the naturalist and theorist of conscientious defiance of illegitimate authority.