Any organization with secrets worth keeping must try to detect spies and repel infiltrators.
It may reduce disastrous false negatives at the cost of an increase in false positives.
In the 1940s, the Soviet Union had hundreds of agents in the executive branch of the US government. KGB records opened in the last 20 years largely vindicate McCarthy (Edit: in that the threat was real; infiltration had happened; most of his targets were Soviet agents, Communists, or associated with Communists; and security risks had to be removed from positions in which they could do harm for the good of freedom-loving people everywhere).
It may reduce disastrous false negatives at the cost of an increase in false positives.
In the 1940s, the Soviet Union had hundreds of agents in the executive branch of the US government. KGB records opened in the last 20 years largely vindicate McCarthy (Edit: in that the threat was real; infiltration had happened; most of his targets were Soviet agents, Communists, or associated with Communists; and security risks had to be removed from positions in which they could do harm for the good of freedom-loving people everywhere).