I don't doubt that the USSR had actual spy operations going on in the US and around the world throughout the Cold War era, just as the US did in Russia and just about everywhere else. Duh!!

That does NOT mean that every accusation leveled by an ambitious politician was justified, any more than every such accusation was necessarily false.

If right-wingers like McCarthy, Nixon, et al, hadn't taken the cynical opportunity to smear their political opponents with transparently fabricated accustations of treason, the general public might well have taken the search for real Russian agents much more seriously than they did. The way things actually happened, when McCarthy was rightly discredited, all anti-Communist efforts and indeed all aspects of counterintelligence were collectively tarred wit the same brush in the eyes of many educated Americans.