Membership to groups can be exclusive or not, in Socionics the two views are in my opinion represented by the Aristocratic and respectively Democratic  attitudes. Aristocratic inclusion is an either/or operation, "you are either with us or not", in extreme cases it can be "either with or against". Why does this happen? What I observe as a rule in the Aristocratic attitudes is consistency, unity and totality , these can alone guarantee the integrity of the group (in this view) and total prevention of undesirable incidents at a social scale. I can see two situations when this integrity can be threatened:
- conflict of practical interests of two or more groups. If the member belongs to both and neither is his "true" group, the unity with each is broken. You can't belong to us but withdraw in conflict, or even worse, take the other side. It just doesn't work like that, the membership would be merely symbolic, in reality meaningless. Membership means a persistent sense of common interest.
- differences in ideology between two or more groups. When ideology defines the Aristocratic group, this group is synthetic and can include members with different interests, however they can't be allowed to have a different ideology than the group, not even partly, because that breaks the group principle of integrity (the ideology is correct entirely), the result is that you don't respect the definition and you are therefore excluded.
I assume few would have the difficulty in associating the two views with the Delta and respectively Beta Aristocratic attitudes. The interesting part to me is that counter-intuitively, the Delta type of consistency is not internal, but actually external and contingent, therefore related rather to Te than to Fi, internal (one's view) is only the sympathy. I can now associate extreme Delta sort of attitude with groups like family business, Mafia, while the Beta one with totalitarian states (Nazi DE, Soviet Union, N Korea) or radical religion. Nationalism, IME, can be of both kinds.
It should be noted that Beta types are highly individualistic, which at a glance comes in contradiction with the idea of Aristocratic type, but it is not. As stated above, ideological groups are synthetic and can include people of different interests and sympathies; as long as their thinking is correct, they can't step wrong but in "trivial" matters, the ones that are not addressed by the ideal. If say this ideal consists only of believing they are the descendants of Atlantis, then they are allowed to do anything but doubting this, everyone who are perceived to doubt or dispute it being banished.
Now what about Democratic attitude? Can't it from groups? Yes, it can , but unlike the Aristocratic one, these groups are perceived fragmented, they have goods and bads, or some may be appropriate/useful today but others tomorrow. The groups, the way such people perceive them, are not integer or definitory, they are merely organizations of people who have something in common. Being slightly (or sometimes) different, in action or thought, is perfectly allowed, since they focus on different aspects, the ones they are interested in and the group satisfies. Having this different view, multiple membership is natural, all relationships being of the same tier, in case of conflict of interests or ideas, they find legitimate to adhere to the one that is the most satisfactory or entirely withdraw, when the conflict does not address their concerns, therefore the concept of "treason" can not be applied.
 - Aristocratic = Beta, Delta; Democratic = Alpha, Gamma.
 - "you're an <identity> before everything", "you were born <identity>", etc.
 - I can't even conceive Gamma without unified effort and collaboration, which are very efficient.