Consider that [investors|police|politicians|priests|religions|banks|unions|wives|airport taxis|pets|corporations|executives] are great in theory and in many circumstances have proven themselves corrupt to the core in practice.
I mentally swapped "corporations" out for "unions" in your sentence and it reads just as well.
I consider it a credit to the anti-union propagandists that we're all so quick to discard one of the very few tools we laborers have to better our lot in life.
No parent comment criticizing unions does it without the implication that they shouldn't exist. This is most easily seen by the total absence of any mention of a specific union, thus direction the objections towards the concept itself rather than any specific version of it.
All unions, as a general concept, tend toward corruption. Just like corporations do. The concept itself is flawed. But flawed does not mean it shouldn't exist.
Unions are a way of concentrating the power of labor.
All power corrupts. The observation proves nothing about unions specifically. If you take away power from unions it just goes and does its corrupting somewhere else.
Saying "the problem is not the unions" is as wide-brush as saying they are the problem; unions have some good causes but the core of their existence is to keep employees employed, sometimes that means important jobs that should exist and sometimes its a cancer that stops a business from profiting or stopping the creation of new ones or the advance of technology (think taxi drivers vs self-driving cars)
Waymo is still developing the technology, they can only go 5000 miles on average without the need for human intervention. They're getting close, but they don't exist yet.
