I don't buy it. What is ultimately showed was that the CP in the USA would subordinate the needs of workers and other folks in the US to the strategic needs of the Soviet Union. You may see that as the right choice - even that preserving a strong Soviet Union was more important than strong leftwing unions in the US - but for those who did not, it discredited the CPUSA and the left in general.
There are many leftists then (and like myself today) who saw nothing superior in Munich over the Hitler-Stalin pact, but saw the willingness of the CPUSA to sell out US workers for the needs of the Soviets as reprehensible. It extended not just to their initial twists in foreign policy but to their rigid support for no-strike pledges during World War II, to the point where conservatives in the union movement ended up looking more militant than the so-called "left-wing." Because of the CPUSA's rigid position on the no-strike clause, even as the capitalists drove down the standard of living of workers during the war, by the time we entered the post-war period, the CP-led left in the union's no longer was seen as the militant wing of the movement. More conservative but more militant union leaders like Walter Reuther were able to take over control of unions like the UAW, leading to the 1948-49 expulsion of the left-led unions.
Which in the end was hardly in the strategic interests of the Soviets. So it was bad on both fronts.
-- Nathan Newman