Not exactly a patriot, but am a degreed historian, so tend to think of things that way.
I do seem to recall, that for all our superficiality, boneheadedness, stubborness, narrow-mindedness, myopia, insularity, and general ignorance of the larger world picture . . .
We do seem to have some good qualities as well. If there is such a thing as a just war, WWII was certainly it. Good guys and bad guys? Just a few words here; Auschwitz, Treblinka, Buchenwald, Bergen-Belsen. That should be enough. Given the realities of the situation at the time, it's not much of a stretch to claim that the world was saved from a very, very dark potential future.
Like it not, we ARE the arsenal of democracy.
Now let the arrows fly.
You claim to be a historian and take such a black-and-white view on WWII? Hitler was evil, no doubt about it, but it's quite debatable whether siding with Stalin was necessarily a good thing. After all, he did kill more people than Hitler.