Fulbright's essential argument was that great nations get into trouble and can go into long-term decline when they are "arrogant" in the use of their power, trying to do things they shouldn't do in places they shouldn't be. He was suspicious of any foreign policy rooted in missionary zeal, which he felt would cause us to drift into commitments "which though generous and benevolent in content, are so far reaching as to exceed even America's great capacitities." He also thought that when we brought our power to bear in the service of an abstract concept, like anti-communism, without understanding local history, culture, and politics we could do more harm than good.
Joe Kristensen, president of the Fulbright Alumni e.V., has compiled several quotes from The Arrogance of Power. One of them is:
Freedom of thought and discussion gives a democracy two concrete advantages over a dictatorship in the making of foreign policy: it diminishes the danger of an irretrievable mistake and it introduces ideas and opportunities that otherwise would not come to light. (...) In addition to its usefulness of redeeming error and introducing new ideas, free and open criticism has a third, more abstract but no less important function in a democracy: it is therapy and catharsis for those who are troubled by something their country is doing; it helps to reassert traditional values, to clear the air when it is full of tension and mistrust. There are times in public life as in private life when one must protest, note solely of even primarily because ones's protest will be politic or materilally productive, but because one's sense of decency is offended, because one is fed up with political craft and public images, or simply because something goes against the grain.
Joe has recommended this book and provided more quotes in the October 2003 issue of the Atlantic Review.