"Episode 39 of Jacob Mchangama's podcast history of free speech. How Weimar Germany, ambivalent about free speech and vulnerable to censorship, quickly gave way to Nazi tyranny."
I can't recommend this highly enough, because Warren's proposal seems to be making the exact same mistake as the one made by the social democrats of Weimar Germany.
http://traffic.libsyn.com/freespeechhistory/Episode_39_-_The...
EDIT: Warren constraining it to just voting doesn't do much to address the lesson here: if the government is put in charge of determining what is true and false, that makes it easier for a fascist government to consolidate its power. This is exactly what happened in Germany in the 1930s. This is all covered in the podcast linked immediately above.
Downvoting me won't stop history from repeating itself. Please listen!