Hundreds of thousands of pages of documents from a number of sources have become available for the first time during the past twenty or thirty years. These include a trove of Soviet diplomatic cables the U.S. intercepted and decrypted for about thirty years, which were published by the Government Printing Office in the mid-1990's. These documents, read together, prove beyond any reasonable doubt that the security threats McCarthy and other members of Congress were investigating were all too real. In some cases, they were even worse than anyone suspected at the time.
Stalin had taken advantage of the lax security that prevailed when the U.S. and USSR were allies during WWII to infiltrate the government with many dozens of people who were in various ways working for the Soviet Union, and against this country. All sorts of departments in the executive branch, including in the military services, were riddled with these people during Truman's presidency. A few of them were outright KGB agents.
I don't know any members of the John Birch Society (I think there must be about a hundred all together) and I doubt many people pay attention to it any more. But it seems to have caught your attention. You are right that there are extremist nut cases lingering on the fringe of society--no doubt about that. They pop up on sites like this occasionally, making furious rants against "right wingers," Christians, people who support gun rights, and anyone else who loves this country and dares question their intolerant collectivist views. These people on the fringe are sort of today's version of the America-hating Reds of the 1940's and early '50's.
I hadn't heard the term "crypto-fascist" in a long time. It's very insulting, and directing it at any other poster would very likely violate the civility standards here. It was Gore Vidal I first heard use that term when, as a guest on William Buckley's TV show "Firing Line," he called Buckley one. The enraged Buckley responded by swearing at him, calling him a derogatory name that referred to Vidal's homosexuality, and threatening to knock his God damned teeth out. Only too bad he didn't.