To my understanding, Chomsky feels that US involvement was justified but that they should have tried diplomacy earlier. What he has been consistent with is his adamant opposition to the use of nuclear bombs, calling the bombing of Hiroshima and Nagasaki "among the most unspeakable crimes in history."Chomsky feels that the justification of WWII is questionable (that the US didn't have a right to wage wars on Japan and Germany). 'nuff said about Chomsky.
I actually agree with him on the latter point - the complete disregard for civilian life (and years of altered genetic health) was unconscionable. And the development and use of nuclear ordinance was history-altering in the worst way.