I question whether the libertarian "left" is really "left" - you don't get to call yourself a liberal just because you're pro-choice and drive a Prius.
The most harm done to workers has been by Democrats (yes, I'm looking at you, Bill Clinton) who pivoted away from the notion that the power of government ought to be a counter-balance to the power of business, and sold out the New Deal to a bunch of greedy, corrupt boodlers.
I'm reading Thomas Frank's new book, and getting angrier by the minute. (I'll post a full review if I can keep from making the entire thing one long blue streak of angry swear-words.)
Revolution may be our only hope.