Good point. A bill of attainder is essentially a legislative act that singles out a person or group for punishment without a trial.
I'd rather have punishment, capitalist punishment, by reducing demand for their propaganda, via trial in the court of public opinion and trial under existing legislation.
A bill condeming someone for some act is not a bill of attainder and it is done all the time. It is not binding.
What would be binding is the revoking of their press pass, and if you don't know if they are working for the enemy, then it is grounds to revoke their pass.