In particular, it's probably no coincidence that Hollywood adopted its blacklisting policy immediately after the HUAC started going after major Hollywood figures. Congress had sent a clear message that the First Amendment did not apply to anyone who was perceived to be friends with a communist, and Hollywood responded with what was probably originally an act of self-preservation.

That kind of authoritarian curtailment of freedom of expression and freedom of association is precisely why I railed against the idea of drawing any lines up above. When we start talking about drawing lines we're implicitly talking about criminalizing a certain kind of behavior. It's the first well-intentioned paving stone in a road that leads directly to tyrannies such as McCarthyism.