When I had a job that was represented by a union they forced us all to listen to the union representative who came in and gave their pro union propaganda to everyone. I was annoyed that they didn’t have anybody to present the opposite point of view.
You only say that b/c you've been really lucky/unlucky so far. Either you don't know what dealing with hostile management is like or you've had really shitty unions. Either way most employees benefit greatly from having representation in the workplace rather than having to deal with a dictator alone.