Weeeeelll … see, here's the thing. In some things, Joe McCarthy actually was right. The Communist Party of the United States of America (CPUSA) was funded by the USSR, and was used by the USSR to commit espionage. Alger Hiss was a Soviet asset. So was Klaus Fuchs. So was Theodore Hall, and so, it turns out, were a bunch of people. Between 1940 and 1945 some 100 Soviet assets worked in the US government, some dozen of them at the State Department. Some of this has been known for a very long time, and some was only made public (or confirmed) in 1995.

But we can still be critical of McCarthyism. At best, McCarthy's crusade to find and prosecute Soviet spies was ineffective. In fact, in some respects it was counter-productive, because its ineffectiveness made it look like there was no such thing as Soviet espionage and increased public sympathy for the CPUSA.

So even when you're right, or partly right, you can still be wrong.