GM's labor costs are high because of pension costs. They promised an entire generation of workers old-age benefits if they gave their life to the company, and now the company wants to eliminate that deal, because they simply didn't plan for it correctly (oh yeah...they also made crappy, fuel-inefficient products that nobody wants).
My grandfather was one of those pensioners. He retired from GM after over 30 years -- having sacrificed his hearing and his back to the job -- and the pension gave him a modicum of comfort until he died. His widow still relies on it to survive. There are thousands of other people just like them, who made a deal with the company in good faith, that the company would just love to revoke.
I think GM should be allowed to go into bankruptcy, but if they do, the judge would do well to fire or eliminate the salary of every executive who failed to plan for pension costs, resisted fuel-efficiency standards, eliminated new product programs, and otherwise destroyed the company. Then, perhaps they can think about cutting the pension benefits of the blue-collar guys who gave their health to a corporate machine.