If you were an ordinary Lefty anytime before 1993 (meaning you are over 30 years old) you grew up never having dealt with any national media or academic environment other than the Left. The first prominent medium to present a non-Lefty position was Rush Limbaugh, the father of modern talk radio. Limbaugh went national in 1993. By 1996 Rupert Murdoch started the first non-Lefty TV network. That still leaves all the major mainstream newspapers and all of academe in the Lefty camp but Americans could finally find a non-Lefty medium if they made an effort. Of course, America did find them and Limbaugh and Fox have the biggest listenerships and viewerships.
Over the past 20 years international news has also filtered into public discussion. To the humiliation of the Left. Communism failed in the USSR and China.
Today there still isn't much non-Lefty media in America, but talk radio and Fox are sufficient to drive Lefties to their peak of anger. You doubt me?
Witness the White House that spent the first month of the new 2009 administration attacking Rush Limbaugh and the 8th through 11th month of 2009 attacking Fox News. I'm not making this up. This is the source of Lefty anger... the mere existence of opposition.
The anger on the Left comes from the fact that a non-Left voice now exists in America and anyone who wants to hear it can.