> What problems are you referring to, specifically?

at the end of the day, unions are still ran by people. So it can be corrupted from the inside or out. They could raise dues on a whim and spend it recklessly instead of saving up for a strike or for other resources needed to advertise.

And union means that non-union (aka new workers to the industry like graduates or people making a switch to a new career) have another layer of beauracracy to go through. Beauracracy with their own whims. Elevator workers pay very well thanks to union, but it also basically means you wont be getting into that industry without knowing someone. So, double the nepotism needed.

Then the last ambivalent argument is that unions can indeed hold back technological progress. It's a hard issue to talk about because that's the exact thing opponents will argue when unions strike, but in some industries the workers have the biggest incentive not to use the most efficient means of work. Especially for businesses that can have slow times or simply run out of work to do. Basically your first point.

the second way is ideal, but we've seen over the decades that efficiency ever rewards the workers. We're something like over twice as efficient as workers 50 years ago, but our buying power has gotten worse, and we work more hours. Companies has shown we can't trust them to achieve that Jetson Utopia of doing an hour of work a day at efficiencies of entire 20th century factories as an individual. Our reward is just to manage 100 factories instead.