[AnthonyMouse]

> On the other hand, my dad was a plumber and his union seemed to bring him real benefit.

Unions for licensed professionals are more lobbying organizations than labor representation. Their goal (which they often achieve) is, effectively, regulatory capture to create a barrier to entry into that labor market and drive up scarcity to increase prices.

It's a similar dynamic to public sector unions -- they're really negotiating with the government, and if the union is large enough then they're a significant voting constituency, so it's like a large shareholder in a publicly traded company using their influence over the organization to have the organization engage in self-dealing with the shareholder's other business.