> See current situation where the Carpenters' Union in California is pushing hard against an initiative that would make it much easier to build more housing in the state because it would also reduce requirements for union labor

If you're talking about AB 1751 (Missing Middle Townhome Ownership Act) I think you have this exactly backwards.

> Unions are very much an in-group vs out-group phenomenon

As opposed to what? You and the GGP phrase this as a dichotomy, but I'm really curious what the other side of this is, because "not being in a union" doesn't erase your self interest or all the many many groups of people doing the same that don't feel like they're apparently being overly self interested by forming corporations, governments, non-profits, advocacy groups, etc, etc, etc