The left in the 30's and 40s definitely did disgrace itself by its sucking up to Uncle Joe Stalin, but you can't spin out of that that McCarthy, and especially his sleazeball pal Roy Cohn, were a minor and aberrant phenomenon even if revisionists like Buckley and Coulter have been trying to rehabilitate them for years. And what the left did back then is really no different than what the right is doing now by sucking up to the Fundamentalist Christians. As for the communist movement around the world, there is no monolithic communist movement, there never was, the left has always been fragmented and divided, occupying a very broad branch of the political spectrum with many differences, including open warfare. The Soviets promulgated the myth of worldwide socialist solidarity to discredit their own critics on the left and to assume the mantle of respectability and authority that goes with leadership.

The McCarthyites and their successors were either stupid enough to believe the Soviets, or smart enough to take them at their word because it suited their own goals.