Chris, there were spies but McCarthy is a distinct issue.
While I have no desire to discuss the Hiss case, although he went to jail and the evidence points to him, the question has never been fully settled.
At any rate, many young people in the 1930s were disillusioned with western life and had dalliances with Communism (whether as Marxists or Trotskyites) but then became disillusioned with Communism and in many cases became very conservative or law abiding people but yet were hounded for the rest of their lives. Youthful indiscretions shouldn't haunt you for the rest of your life. I should know; my Father was going out with a girl in the 1930s and she invited him to join a Trotskyite group. He quit after a week, thinking it stupid. That's what people did back then; they were interested in new things. Just imagine if that had come out. Heck, I probably wouldn't be here today. That is what McCarthy tried to do: use people's interest in new things against them. That is why I hate people like him.