The most censored subject is obviously the subject of censorship itself. The reader does not know that the list he sees in front of him has been censored. They are not open about this. They effectively hide this information from the reader. Since most readers do not submit anything, they are not aware of this. It creates a curated world in which they believe that they know what other people think. This is a wrong belief, because all other opinions have just been filtered away.
The linux journal had a great post on how all these walled gardens as destroying what the internet was.<p><a href="http://www.linuxjournal.com/content/whats-our-next-fight" rel="nofollow">http://www.linuxjournal.com/content/whats-our-next-fight</a>