“Men of intellectual and moral eminence who encourage public disobedience of the law are responsible for the acts of those who inevitably follow their counsel: the poor, the ignorant and the impressionable. For example, to the professor objecting to de facto segregation, it may be crystal clear where civil disobedience may begin and where it must end. But the boundaries have become fluid to his students and other listeners. Today in the urban slums, the limits of responsible action are all but invisible.”