Are oppressive governments threatened by the freedom of information?

In this thread,
http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=157615
the concept is expressed that various tyrants would be threatened by information being disseminated to their populaces.
Is this true? Can giving opressed people open channels of communication and learning free them? I had always assumed that trying to quash free speech/free listening was a mark of arrogance and stupidity on the part of said tyrants, but have no cites either way.