This isn't my primary area of focus, but one relavent thing to keep in mind is that the second Red Scare was close on the heels of the Great Depression. Durring the Great Depression it was quite common for people, especially wealthier or more educated people, to be at least interested in learning more about Communism as the common perception at the time was that the USSR was not suffering from the Depression as most of the rest of the world was. Therefore, if one was looking to put another in a bad light in the US at the time, it was fairly easy to show that a person had attended a meeting of their local Communist party or had bought a copy of the Communist Manifesto. While this seldom if ever meant that the person was actually interested in communism, it was an easy target for those looking to slander. Hopefully someone with more knowlege of the subject can ellaborate.