The Fairness Doctrine was originally imposed when we had very limited broadcast television/radio programming. It was actually requested by conservatives - who felt their interests were being underreported by the major media outlets of the time, ABC, NBC, CBS, PBS. In fact, prior to the Fairness Doctrine - the only national opinion outlets in broadcast media were the last five minutes of national news broadcasts - such as Walter Cronkite or Howard K. Smith editorials in the last 5 minutes of the Evening News.
As the Cable Television revolution progressed in the 1980's - along with the deregulation of the AM/FM radio spectrum, the Fairness Doctrine became obsolete because many more options became available. People were no longer tied to traditional network news outlets for their news and opinion programming.
The bottom line is: Fairness is established in the Broadcast Media by the different choices available to audiences. Applying a "fairness" standard to individual stations amounts to an unfair regulation of radio station programming - regulation which is clearly unnecessary in today's radio marketplace.
For those who cry that there is not balance between differing viewpoints - or that "talk radio" has too much influence over today's citizenry should spend their time reinforcing their own ideological arguments rather than trying to tear down the means by which their political opponents share their views.
NPR - although somewhat (not completely) publicly subsidized - has survived, and even thrived thru deregulation.
Air America has failed to achieve the audience and broad-spectrum appeal of its conservative counterparts not because of a "lack of fairness" - they had plenty of opportunity to gain audience share and to spread their "message" - but they failed to provide competent hosts able to express a compelling message to any audience. Alec Baldwin, Al Franken, and others are examples of failure. On the other hand, Tom Leykis (sp?) has been successful for nearly as long as Rush Limbaugh, if not quite on the same economic scale.
When Congresspersons such as Trent Lott (R-MS) and Nancy Pelosi (D-CA) start talking about the "Fairness Doctrine" - what they're actually talking about is trying to punish success on the part of leading conservative talk radio personalities.
Given the conservatives' success in converting new believers to their cause in the past two elections, I would think the liberals would prefer to keep the status quo. It's working for them.