I had a boss who was an expensive consultant for unions. He explained the reason unions in the US were shrinking is that they are too powerful. They control huge pension and healthcare portfolios and can completely control the relationship with employers, especially in closed shop situations. Comparatively, European unions are much "weaker" - or maybe more accurately their purview is much smaller. They control smalle…
I think you'd be hard pressed to find anyone pro union who'd say unions have too much influence or sway in the lives of US citizens. Most workers don't have union representation and unions don't have much say in worker pay in a great majority of sectors. Especially where it could help like warehouse work which has seen wages plummet with the advent of Amazon.
Now, compare that to two unions which are extremely powerful and not always good for the public or their members!
1) Teachers unions. Extremely powerful (at least Oregon where I know about them), but they don't necessarily help teachers! Pay is low because they haven't flexed their power and are fully at the whim of taxes. Since their funding is low the most teacher's union can guarantee their workers is that they will have a consistent job. Which sucks! Also, when COVID occurred there was little room for teachers to get a say as to how classes would be virtual, when kids would be back in schools, or when and how the mask mandate would be lifted. Supposedly a union would help!
2) Police unions: super strong, extremely political, extremely effective. Also nigh impossible to fire a cop unless they offend their union or a fellow cop. Rarely do police budgets ever get cut or does cop pay go down. Do most folks want this? Do most people in New York want their police force to have a budget larger than military of a mid sized country? Probably not? But hey, they're too powerful to do anything about.