Define "societally best outcomes". By using the word "societally", you are saying it's not he best outcome for the business, nor is it the best outcome for the employees, nor the best outcome for the customers, but the best outcome for the society at large. Your MTA example shows that a union is great for workers. Please explain.
Considering unions are used successfully in many industries and are supported by both major parties in the US, you'll have a difficult time explaining how they are all wrong.
> Smaller and wide set of unions in an industry can be effective,
Isn't this the KickStarter union?
Also, what's a "Smaller and wide union"?
Finally, if unions are so bad, why do many of the largest companies in the world continue to hire from unions?