Unions began to help workers from being taken advantage of by robber-baron manufacturers, so the workers would get a fair wage and a fair share of benefits for the work they do. However, the last 30 year or so has seen labor unions redefine what is "fair" to "get everything you can and threaten to walk out on the job if you can't negotiate a contract to give a worker with a barely-earned high school diploma $27/hr to work on an assembly line tightening four bolts, four weeks vacation, and Mickey Mouse's birthday off." During the high times of the 90's, the manufacturers were happy to oblige without thinking long-term, and unfortunately in created a sense of entitlement to the union workers.
I live in Southeast Michigan, half the blue collar jobs are Big Three or OEM supplier assembly line jobs. A friend of mine worked for an OEM supplier a few years ago on the line, and when he started his union steward told him to go in the break room and watch TV when he finished his daily quota. Some days he actually worked on the line 3 hours during an 8-hour shift.
My bank manager is friends with a local Ford assembly plant manager, and he told her when he started at the plant, he had to put a stop to a group of line employees bringing in a barbecue grill every day into the plant, on the floor, making hamburgers and hot dogs and selling them to the other workers. Of course they complained to the union steward and the old manager looked the other way, but the new guy wasn't scared of the union.
The combination of management failures and union greed produced the current problems, and once GM or Ford is "shut down until the cows come home," will the union help all those people find new jobs? And who would want to hire a worker that is used to getting paid eight hours when he works for three?