Old Chinese proverb: If you save someone's life, they will hate you
forever.
Grateful as we were for the US help in winning WW2 (when you finally
got around to it) we are obliged to be even more grateful to the
Russians, who did the bulk of the work.
Of course, the Russians didn't have a lot of choice about joining in,
since the Germans chose to invade their country.
Since the U.S.A. was never invaded by the Germans, you could perhaps
have sat out the European war, but only at the expense of seeing
Europe becoming part of a Russian empire. Roosevelt's administration
had enough sense to realise that this wouldn't be in your national
interest.
Since we owe the Russians a larger debt of gratitiude, we presumably
ought to hate them more than we hate you.
In fact nobody hates America (with the possible exception of Osama bin
Laden and his colleagues) but we do think that you ought to get around
to cleaning up your act sometime fairly soon.