Unions were great at stifling innovation and destroying some of our former industries such as Steel and Automotive - see what's left of former very wealthy Detroit. The classic example is the unions not allowing the Toyota Lean Production system in, as then you would need fewer workers. So in not allowing innovation, the unions were key factors in destroying entire industries which have now been built elsewhere. If t…
But this isn't a forgone conclusion, for example worker relations seem to work fine in general in Germany which has actually institutionalized worker representation at a fairly high level in corporations.