A) If the union has a good chance of increasing wages 400 to 600 per year locally, then that is a great deal for the union organizers, a passable deal for the workers, and a bad deal for Amazon. I didn't say they won't be able to raise wages at all - just maybe not enough to justify the $500 union fees.
B) Not every state is a right-to-work state. So, from a 'worker's of the world unite' perspective then obviously making a union in Alabama will help other places form unions.
I could be very wrong and perhaps the union could get 1 or 2k more per year - but I am skeptical.