Living in Detroit and knowing a lot of people who work in the auto industry I can tell you that for every ounce of goodness that comes from a union there is an equal and opposite ounce of badness. The shit that I hear people get away with is remarkable. And yet they continue to come to work day after day with seeming impunity, continuing to assemble vehicles, etc...
I am personally anti-union because inevitably they become so large that they succumb to their own internal forces and become beurocratic and misguided.