If you are in the hobby of model airplanes, IMO you should WANT to join AMA.

I collect Lionel trains, I am a member of the TCA & LCCA.
I used to race cars, I still keep my SCCA & NASCAR memberships.
I duck hunt, DU.
Got a Harley, HOG.
Shoot guns, NRA. Grand Dad, gave all the boys life NRA memberships.
Surf, TGSA membership.
R/C cars, ROAR.

I think if your in a hobby, support the national org.

Now that I think about it, if I stopped all my other hobbies, I could join the Ferrari Club.