Unions played an important role in protecting the working man (women generally didn't work way back when) with some sense of job security and things like fair pay, retirement assistance and health benefits.
But that was almost 100 years ago. The real downfall, in my opinion, started when public employees started to unionize in the 50's and 60's. My mother was a school teacher while my father was a school principal. She was protected by the union (really the Massachusetts Education Association) while my father, as an administrator wasn't covered.
She's made out really well, thanks to the union. She retired almost 35 years ago and collects her full retirement, one half of my father's retirement and gets free medical.

The ironic part is that she only taught about 25 years or so total but has been collecting for many more than that.