I have been having a lot of comments disappear lately from Disqus-run comments sections, comments which were topical, non-abusive, and had no profanity. Comments which should not have disappeared. It occurs to me that I have no idea who runs that company, or what their political allegiances are.
The most effective use of propaganda is simply limiting who can speak, while allowing a lot of speech, such that it appears only the major ideas in play have any validity. If you let A, B and C talk as much as they want, and encourage them to disagree mildly at times on unimportant topics, then nobody notices that D has been cut out entirely, and has a radically different, and vastly more accurate, worldview.
In a competition of ideas, the best ones win out. But if the best ones don’t get to play, they never have a chance.