To be a member, a religion may insist that it is impossible join. A person can only be born into it. Or they may insist that only through the mother can one become a member.
I suppose every religion should have a right to be exclusive. Is this discrimination? Perhaps maybe even immoral and shows an inconsistency in the teachings. Of course inconsistency is not necessarily a bad thing. As Oscar Wilde has noted: Consistency is the refugee of the unimaginative.