For Union critics: If you believe unions ever had a positive role; when do you believe it was?

It was to increase the working conditions of the workers from sweatshop conditions in the 70s after the Depression made paying crap wages so easy, but went wrong when the pay increase demands never stopped! And went REALLY wrong when unions ignored the big picture of if the company could afford to pay in favour of using strikes and blockades as threats for money. Blackmail in other words. Balance. All things must balance, even union demands.