"... our primary motive is unquestionably political. It is to make clear to the whole Free World that we will assist any nation that asks for our help in defending itself against Communist aggression." For this to occur, at a minumum the U.S. must demonstrate the superiority of its military power. "To do otherwise would enormously diminish American prestige around the world and cause others to lose faith in the tenacityof our purpose and the integrity of our promises."
But the U.S. position in Vietnam may not allow the achievement of these aims. The political situation in Saigon may continue to crumble. The movement of North Vietnamese troops could make the use of U.S. troops unavoidable. As long as the North Vietnamese believe victory is near, they "would probably be willing to accept very substantial costs from United States air action." The introduction of U.S. ground troops would put the U.S. in the same position as the French, open the door to significant criticism at home, and invite a counter escalation by the North Vietnamese. The entry of Chinese troops would raise the specter of the use of nuclear weapons. Because of the willingness of the North Vietnamese to resist, the scale and intensity of U.S. attacks involve considerable risks of escalation.
"... it remains to be proved that in terms of U.S. prestige and our world position, we would risk less or gain more through enlarging the war than through searching for an immediate political solution that would avoid deeper U.S. involvement."
Ball describes the reaction to his memo:
"When I completed the memorandum, I sent it to Secretary McNamara, Mac Bundy, and Secretary Rusk. Bob McNamara in particular seemed shocked that anyone would challenge the verities in such an abrupt and unvarnished manner and implied that I had been imprudent in putting such doubts on paper.... My colleagues were dead set against the views I presented and uninterested in the point-by-point discussion I had hoped to provoke. They regarded me with benign tolerance; to them my memorandum seemed merely an idiosyncratic diversion from the only relevant problem: how to win the war." McGeorge Bundy said: "I never found his picture of the alternative very persuasive, or, indeed, persuasive at all."
(Source: William C. Gibbons, The U.S. Government and the Vietnam War: Part II: 1961-1964, Princeton 1986, 360-362)