When I was much younger than I am now, I got a job at a construction site. I was told that in order to work there, I had to become a member of the union. So, for about 1/2 month's salary, I became a member in good standing of the International Brotherhood of Hod Carriers and Common Laborers (true!). I didn't see that being a member of a union had any benefits for me.
Of course, I was young and dumb, and I didn't know how unions had been formed to protect workers from rapacious business owners, and had created a system with some muscle so that businesses had to pay attention to workers.
So, why is it that, having learned that, I still don't like unions much? The answer comes, as it so often does, from literature. George Orwell, in writing Animal Farm, has a group of animals who rebel, kick out the humans, and take over the farm. The pigs, being bright, kind of spearhead the thing and become the first among equals. At the end of the novel, the pigs invite humans onto the farm again, and the other animals, looking on, realize that they can't tell the pigs from the humans.
So it is with unions. The auto makers are run by arrogant, short-sighted, overpaid, and fatally stupid men, but my assessment of the unions is that you could swap CEO's about between auto makers and unions and not notice any change at all. So, if you don't like the auto makers, you also gotta not like the unions.
I think Orwell's choice of pigs in the novel is genius.