The Axis Powers had a security pact. An attack by Japan on the US would allow Roosevelt to enter the European theater, which, you are correct, is what he wanted to do. 
 
He did not use the U.S.S. Panay as an excuse for war because his main motive was to marshal US public opinion, which before Pearl Harbor was over 80% opposed to entering the war. 
 
You have not addressed any other real point.

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