The very structure of traditional societies generates the need for functional groups. For instance, it is not easy for a member of a traditional society to lend money to another member of the community, for their relationship is regulated by a higher, non-economic law. In such societies, interest rates are usually quite high given the absence of a rational banking system. The same applies to prostitution. If a man wants to use a woman for temporary pleasure, in other words, if he wants to instrumentalise her, it is very difficult if she belongs to the gemeinschaft, and he has a sense of her sanctity and humanity.
Mercenaries are another example.
Members of the host society can also enter rational, contractual relationships, unfettered by human considerations, with members of the functional group. As outsiders, members of the functional group can perform their function efficiently without subverting the solidarity, social harmony, cohesion and values of the host society, and while preserving the boundaries between sacred and profane. The relationship between the host society and the functional group is not seen as that of exploiter and exploited, but rather as a fair, rational, contractual relationship in which each party achieves its objective. The society's purity and harmony is preserved, the function is accomplished, and the functional group achieves economic survival and preserves its identity. The utilitarian, contractual relationship persists as long as both parties to the contract need each other.