Association groups like the NRA are chosen voluntarily and being a member of such a group may help an individual express or even develop particular aspects that they feel are part of their identity, but as a member of a systematically oppressed social group such as females or hispanic-americans, the identity forming that occurs is not always voluntary. Society places individuals in these categories, and regardless or whether or not the individual actually identifies with this group, he or she is still subject to the systematic oppression that the group is faced with. There is no way to ignore or deny situations you are placed in where you are unable to act in any direction. This oppression is identity forming. Individuals exist not only as mental beings, their experiences shape who they are as well.
Oppression can have a very strong inflence on one's life.
So, as members of a social group, individuals' identities are formed in ways and because of circumstances that are much different than the way that being a member of an association group helps to form identity.