FDR wanted to help Britain and France to defeat the German invasion, but he met strong resistance from both the public and the congress. The anti-war voice was loud and clear, like today. FDR did strengthen the defense to prepare the military for a potential war. America was forced into the war after the Pearl Harbor. According to those conspiracy theories, FDR knew about the attack ahead of time, but he didn't prevent the attack so that he could find an excuse to go to the war. Haven't we heard similar theories about Bush knew about the 9/11 ahead of time and no WMD in Iraq?
FDR did take America to the war and we did suffer huge casualties. In the end, Hitler failed to conquer the world and America has become a super power after the war. Looking back, FDR made the right call to go into the war.
Bush took America to the war and overthrew a dictator. As to what that has brought in the short run, we are witnessing it everyday. However, as to the long-term impact, we can make wild guesses, but no one knows for sure.
Shall we let history make the judgment on whether this Iraq war is worth fighting?