Benedict J Fernandez's "In Opposition: Images of American Dissent in the Sixties" is a kind of pictorial primer of protest, both for and against whatever the cause-Vietnam, fair housing, white or black power , student sit ins. Convinced that people who feel strongly about anything should make their voices heard in "the marketplace of ideas"—the variety of demonstration techniques, indoor and out, this restless decade has produced- Mr. Fernandez has made a specialty of being around when they do and taking pictures to spread the word and the sense of indignation further through exhibitions and publications.