...in the sense that he was right, about the deep web of Communist-sympathizers and spies, embedded in our Eastern intellectual set, and their Hollywood-entertainment counterparts. Some of the techniques used to force informants to "spill" on their families and friends, were heavy-handed and wrong, but the idea that there needed to be an investigation and uncovering of the plot(the Rosenbergs were passing nuclear secrets, for God's sake, and Hiss was a high-level political figure with access to practically anything we might wish to keep secret from our enemies) was 100% correct.
"Blacklisting" was unnecessary, of course. Infiltrating and keeping track of known Communists and their contacts would have been more fruitful, and far less socially antagonistic, even to the anti-Capitalist, anti-American, pro-Stalinist nutjobs who comprised the worst of the dupe-brigade.
The thing is, McCarthy didn't know how deep the Plot was, and exactly how much danger the Reds posed to the American government. His plan was to blow the lid off the whole thing, and he succeeded, only too well. He created a backlash, that many shocked, disbelieving Americans were too quick to join.