As i see it, Unions are groups of employees where they have agreed to cooperate to get a better group outcome than they might be able to negotiate individually. It often caps the outcomes for the very very best, and raises the outcomes for the very very bottom. But across a wide swath they are earning more, or treated better, than they would be had they tried to do it alone. TBD if the union fees negate more or less than this gain.

IMO Cooperatives are a better model, it combines cooperative behavior with the dual risk/profit model of entrepreneurship.