For me, it is all anecdotes from my dad (some of which I observed first hand). He worked for unions for half of his career and then intentionally uprooted us to move to a right to work state purely to escape the unions. He moved up the ranks and ended his career as the general manager of a manufacturing facility. The next county over was heavily unionized. The contrast in the two counties was notable. The industry in the unionized county was run-down, falling apart, constantly in and out of bankruptcy.

The industry in the non-unionized county was literally some of the best in the world in what it does. The plants were clean and well run. Early on in the management-part of his career, my dad hired some formerly unionized workers who had moved up from the unionized county in order to find work (jobs were disappearing in that county due to the bankruptcies). They were fired in a few months because they wouldn't show up on time, were constantly dropping the ball, etc. In his opinion, their work ethic had been ruined.

I'm actually not anti-union, but I'm mostly anti US union. I think if we adopted a non-antagonistic model similar to Germany, it'd be alright.