FDR on public employee unions
Here.
States legalized these unions because Democratic politicians saw it as a method of mainlining political power and political loot to themselves.
Ironically, Jerry Brown, currently hanging on the meathook of California unfunded liabilities, is the one who personally forged that meathook.
Arnold, after his first election, attempted to rein the unions in. The unions destroyed him, both politically and personally. The man hasn't seen his balls since.