Espionage efforts are one thing, but when people are jailed for "inciting rebellion" for the "crime" of distributing the writings of Karl Marx, the undeniable fact that there were lots of spies here (as we had lots of spies there) falls so far short of justifying the sorts of abuses that went on.
The government argued that the Communist Party USA had no right to spread political ideas in the US, and targetted lawyers who dared to defend them.
Whatever the extent of Soviet spying in the US (and it would have been extensive for obvious reasons, as with the other side), the McCarthy era was an assault on the foundations of democracy in this country. If you want to justify that because the threat is real, I suppose we should just give up on this whole Constitutional Rights thing....
Of course, there is no moral equivalence between US spies and Soviet spies, since there is no moral equivalence between subjugation to the totalitarian soviet state (which soviet spies were fighting for) and the liberal democratic capitalism of what remained of the West.
Violence is a nasty thing. But violence in service of slavery is a far nastier thing than violence in defense of human rights and freedoms.
Actually, that is what Yates v. United States turned on and why after the Supreme Court said that distributing literature could not be sufficient but must be paired with actual concrete steps to make it happen there was only one further conviction under the Smith Act (for a Communist Party member who was also a martial arts instructor).
Read Yates v. United States. The conviction was reversed and it brought an end to Smith Act prosecutions of the Communist Party.
Yates also largely overruled Whitney v. California (and set up the formal overrule in Brandenburg). It is worth noting however that although the Supreme Court (this was decades before Yates) held that Communist Party membership itself could be subject to prosecution, Brandeis's concurrence apparently lead the governor of the state to pardon Whitney.
The government argued that the Communist Party USA had no right to spread political ideas in the US, and targetted lawyers who dared to defend them.
Whatever the extent of Soviet spying in the US (and it would have been extensive for obvious reasons, as with the other side), the McCarthy era was an assault on the foundations of democracy in this country. If you want to justify that because the threat is real, I suppose we should just give up on this whole Constitutional Rights thing....