Of course liberals support/justify it since they'll go along with any dumb shit their government supports.
This seems like more an attempt to smear anyone not going along with your ideological narrative about a very straight forward issue.
RT is Russian owned propaganda television, it is now registered as a foreign agent which in no way effects it's ability to say anything. This is a pretty straight forward issue that you oppose for reasons that are either a fanatical devotion to the american constitution or because you like what they say and are concerned that people will watch the channel less because they somehow didn't already know that it was Russian propaganda.
The US government has as much right to do this tiny slap on the wrist to RT as the Russian government has to do the same to Voice of America. In neither case is this really about freedom of speech, it's about the spread of propaganda for ideas we like or dislike by a foreign government for it's own ends.
RT-America's journalists are American citizens, noob.
By that argument any regulation against a corporation is an attack on the personal freedoms of individuals working for that corporation.