And as long as the rational for disallowing does not violate federal discrimination statutes,
a 501(c)(3) can certainly do this.
This is indeed an important point. Look at it this way:
Is AMSAT the National Association for Amateur Satellites in the United States, sort of a parallel to what ARRL is for Amateur Radio?
Or is AMSAT a private club?
If they are a private club, they can do what they want. If they want to be the National Association, they need to meet a higher standard and represent every ham in the country.
A past AMSAT president asserted that AMSAT was the Global association, and National Associations like AMSAT-DL were its organizational members. If that is really the case, the standard would need to be even higher.
Thanks
Bruce