As a counter example, police unions seem to have played a large role in creating/perpetuating the problems so many have been protesting lately.
(You could argue that I'm engaging in a "True Scotchman", but see this article [1]:
> Police unions make it nearly impossible to fire bad cops and incentivize protecting them to protect the power of the union. A police union is not a labor union; police officers are powerful state agents, not exploited workers.
)
[1] https://medium.com/@OfcrACab/confessions-of-a-former-bastard...
Like teacher's unions.