The union workers I grew up around weren't liberals by any stretch. They were Archie Bunker (and I mean that in a good way). Since the early 1980s, though, their unions have abandoned putting workers first in favor of putting leftwing ideology first. The result has been a massive exodus from the union shops into non-union companies.
But the unions have also done a disservice to the entire middle class. By concentrating on politics instead of labor issues, the AFL-CIO and other big unions have favored policies that destroy middle class jobs. In a sense, they suffer from the same problems abortionists do--they're killing their own.
The WSJ has an insightful, short analysis of the problem:
[The AFL-CIO] became part of the ideological left and its regulatory and high-tax agenda. So instead of favoring oil drilling in Alaska, which would create thousands of new middle-class jobs, Mr. Sweeney's shop leaned toward the rich liberals of the Sierra Club. And while many union members are cultural conservatives, the AFL-CIO has spent its scarce political capital fighting conservative judges. No wonder millions of workers look at union organizers and shrug.
While I don't necessarily favor a major move back into unions, I do wish that what remains of the labor movement would return to its original purpose and let Hollywood liberals fight their own battles.