Upvote:0
It is not possible to know for sure.
If by the Red Scare, you are referring to the House Committee on Un-American Activities, it definitely had a chilling effect on Nazi and Communist political efforts in the United States. Many Nazis and hundreds of hard-core Communists from all walks of life got shunned by American society due to the stigma of being summoned before the committee. There were also a lot of knock on effects, such as the disgrace of J. Robert Oppenheimer, who had run the Manhatten Project during the war. It is suspected Oppenheimer funneled Soviet agents into the project so that nuclear technology would be transferred to the Communist bloc, but did he actually do so? It is hard to say.
Some highly notorious spies were outed by the Committee. For example, Harry Dexter White, an important government official in the Roosevelt administration funneled huge amounts of secret US information to the KGB and illegally diverted funds from the US Treasury to buy armaments and food for the Soviet Union without the knowledge or consent of Congress. Dexter also probably insinuated Soviet spies into the United States and placed them in positions where they could collect intelligence. None of this was discovered until many years later, but the HUAC named and shamed him in 1948.
As T.E.D. mentions the point of the HUAC was not to catch spies. It was to suppress Nazi and Communist sympathizers who advocated the violent overthrow of the US government and its replacement by a non-democratic alternative.
Upvote:2
The Red Scare was not about catching actual spies. The USA already had law enforcement agencies for that task. Instead, it was about finding and publicly outing potential spies. People who might be sympathetic to the Russians (or vulnerable to blackmail by them), and thus might in the future commit an act of espionage, if given the chance. For instance, during this era this logic was used to fire an astounding amount of people from government jobs for h*m*sexuality (at its height, it was about 2 a day).
By and large the people pushing the scare were looking for publicity for themselves. An actual spy doesn't help that cause all that much, because the bulk of the publicity surrounding their case will go to government enforcement agents and lawyers.
If you aren't one of those, by far your best target would be someone who can't actually be proven to have committed a crime, so you can just keep bashing them yourself as long as the media will listen to you. Even better if its someone famous, or someone that some people will want to go to the news to defend. That will help feed the story.
I don't believe there is a good way to measure how many (or if any) incidents of actual real-life espionage this might have prevented. Its possible that fear of the witchhunt itself made government officials vulnerable to foreign agents, so it may have even been negative. There's really no way to tell.