In A People's History of the United States, why does Howard Zinn feel that Wilson made a flimsy argument for entering World War I?

"War is the health of the state," the radical writer Randolph Bourne said, in the midst of the First World War. Indeed, as the nations of Europe went to war in 1914, the governments flourished, patriotism bloomed, class struggle was stilled, and young men died in frightful numbers on the battlefields-often for a hundred yards of land, a line of trenches. --Chapter 14, Page 350, A People's History of the United States

Howard Zinn outlines his arguments for why World War I was fought in the opening paragraph of Chapter 14 (referenced above). The nationalism that was created by the Great War benefited the elite political and financial leadership of the various countries involved. Socialism, which was gaining momentum in Europe, as was class struggle, took a backseat to mobilizing for war. Zinn believes that World War I was fought for the gain of the industrial capitalists of Europe in a competition for capital and resources. He states that humanity itself was punished by the sheer death and destruction of the war for no benefit.

The United States, behind Woodrow Wilson as president, had pledged neutrality. Wilson would change his stance as the war raged on. The US economy was hitting a low point when the war started. By supplying Great Britain and France with munitions, the American economy was gaining momentum. Germany, for its part, did not want her enemies being supplied with materials for war and started to torpedo American ships. Wilson used these attacks on American ships as a justification for warfare. He made the following statement:

"I cannot consent to any abridgment of the rights of American citizens in any respect. . . ." Page 361, A People's History of the United States

This statement, of course, does not make sense. The reason that it does not make sense is because the British were infringing on the rights of American merchants throughout the war. The fact that the United States benefited economically through trade with Britain would preclude the possibility of war with the Allied Powers.