… is from page 159 of the 1964 Harper Torchbooks edition of Karl Popper’s 1957 The Poverty of Historicism (original emphasis):
If the growth of reason is to continue, and human rationality to survive, then the diversity of individuals and their opinions, aims, and purposes must never be interfered with…. Even the emotionally satisfying appeal for a common purpose, however excellent, is an appeal to abandon all rival moral opinions and the cross-criticisms and arguments to which they give rise. It is an appeal to abandon rational thought.
