On a related note
There is some evidence that contemporary liberalism's need for a more vigorous propaganda is already being acted upon. Remember the calls for a "liberal Rush Limbaugh" or a "liberal Fox News"? If you view Rush Limbaugh and Fox News as purely Right-wing propagandists that also happen to be beating you like a drum in the court of public opinion, your need for an equal and opposite counter-attack becomes obvious. Or examine the utter conviction of many liberals that the mainstream media isn't liberalism's propaganga wing: if any "Joe blogger" on the internet can pick up a copy of the New York Times and punch a bunch of logical holes in its storylines, obviously there can't be much propagandizing taking place.