I can only go off of what I have seen.
First off unions if ran well and ran with both the company's future and the workers interest at heart I will support. Always have.
But what I have seen is usually the opposite. I worked in the metal finishing industry for years. The shops I worked in were owned by the same family. One (the father's) was union, the other (the son's) was not. At the fathers plant as a union member if you were plater or a racker that is ONLY what you did. If the other had nothing to do, they DID NOT assist the other out. One, they didn't have to, and two, it wasn't in there job description. So there were times I saw a lot of guys just standing around for an hour or so with nothing to do because they didn't have to. Now the benefit to this is your job is secure...only you can do that job. No one else can do it. But if you called in sick and another "plater" was not on hand to fill your role because they were ahead of schedule (which never happenned) you would have an entire production line shut down. You would have the racker come in, do 1 hour of work on that line and then shift over and help other rackers load up and increase their stand around time. From a company perspective this is a lot of down time and wasted money. However this union never had any laid off. The company also used a lot of temps for menial tasks (paying an agency 11 an hour for 7 an hour labor) because the temps could be freely shuffled. I also saw old timers receive raises for time in and not performance. I could out produce all of them yet all of our raises were the same. I moved on when the son openned his plant...a lot of us younger guys did, because we would carry a huge brunt of the production.....after the son's shop opened up the father sold his 5 years later as his profit margin was slowly dwindling due to union costs (pay and such) yet production never increased due to the lock step of who could do what or was able to be asked to do what.
Move on to the new plant. I excelled. Management saw my expertise, knowledge and potential. I learned and did everything I could. Overtime was offered to those that wanted it at any position, if not enough rackers took the overtime platers could fill the roles and get OT at their pay rate doing racking work to keep production going. Some of the guys from other [plants didn't like this as they came over from union shops and loved it...they saw their Time in the field as a right to higher pay instead of their performance. We all had some gripes early on on how some things were ran as well so union talks started. The owner sat down with each one of us, found out our complaints and changed things...not all but the one's that made sense, so union never made it in.
I eventually (in 3 years) went on to become management at this shop. I didn't have the most time in. I didn't have the most experience. But I knew everything and proved myself. I Always did R&D. I studied things and every trade show or seminar I signed up for to go. I even learned the waste water management side of things. I learned the laboratory/ chemistry of everything (incidentally a metal finishing shop is a terrorist's dream) I helped out the repair/maintenance crews to get an understanding of how things operated and could be repaired. When I was offerred the management position I was given just shy a 6 figure income (on High school diploma mind you) if you include all the benefits. I was making almost as much as the plant manager. But I was 2 steps under his position.i made more than his second/assisant manager. Why? I ran the night crew. If my guys stayed late or worked overtime, I stayed with them. If something broke down, I did not call/page the on call head of maintenance to come in a spend 5 minutes to fix something (giving him an automatic 4 ours pay and waking him up in the middle of the night). I fixed it myself. I did not need our wastewater management guys to do anything for me as I could do it as well. They didn't have to work any overtime to ensure my shift had proper waste handling because I could do it. In a union this would not have worked, In a union I would not have been given the position as I did not hold seniority. In a union the company could not have fully compensated myself to do all this as they would have to pay three people to do it....But since it was not union, I got the job and got paid very well.
At some point I will give my wifes experiences in the postal union, but this is enough for now.
Unions have their good points, I will say that, but unions can also cripple a company considerable and hold some more deserving back over those less than...