RE: Alternate to AMA
Non-AMA members cannot be FLYING members of an AMA club, for insurance verification purposes.
It is up to the club whether or not to allow non-AMA (and by extension non-club) members to fly at their field. It's highly discouraged, I believe, again for insurance verification purposes. I as a club officer am not going to stand guard, or post guards at each of our fields 24/7 to stop each and every non-member and ask for their homeowner's policy to make sure they're covered. A mere mortal probably couldn't tell if the policy covered R/C flying anyway, and then I have to call their provider and verify that the policy is paid up.
Since AMA club fields are generally on PRIVATE property, there's nothing you can do in a court of law to force them to accept non AMA members. You might have a leg to stand on with fields on public property, but you'd have to go after the governing body in charge of that land, since it's normally an agreement between the club and the county/city/state regarding AMA and/or club membership.
In this whole thing, the club isn't trying to force anything on anybody out of maliciousness. They're trying to protect themselves and their flying privileges as best they can.