The terms right-wing and left-wing (or liberal and conservative) are practically useless. Today's corporate-fed conservatives piously pose as the heirs of the founding fathers, without realizing that Jefferson and Madison (the architects) considered "the monied incorporations" the greatest threat to democracy. Today's govt. "liberals" are just as indebted to their corporate benefactors.Richard Nixon, a "conservative" who expanded the welfare state, was closer to the spirit of the "radical" Thomas Paine (who advocated a "senior security" fund) than Bill Clinton, a "liberal" who went out of his way to "end welfare as we know it".
Power, whether political, economic, cultural, etc., moves down and up more than right and left. Folk music has long been the voice of those without power. It has been, for the most part, handed down through the generations by those who felt the oppression of aristocracy, southern 'Jim Crow' culture, or whatever thumb is lived under. It only seems leftist by today's blurred definitions. Whether it's Woody Guthrie, Bruce Springsteen, or Rage Against the Machine, these folk (until I hear a horse sing) artists that sing about these topics are only shining a light on the injustices power can wield.
As for those in power, they can always hire a Haydn, John Phillip Sousa, or material (re: corporate) girl to write their music.