Claim. Because the four-position-foundation is centered on a unique, unchanging, absolute origin of love, fidelity in every family relationship must be absolute — invasion of any one relationship destroys all of them.
Elaboration. SMM grounds family ethics in the unicity of the love origin: “The four-position foundation refers to a parent-centered origin of true love… The origin of this love is unique, unchanging, and absolute. However, love does not exist only in God or only in the father or mother. It comes about on the foundation of the family – a true family!” (CSG 15.2 §1, 106-57, 1979.12.9). The fidelity rule follows: “Fidelity in such a love-centered family requires that love be absolute. It is absolute in all its relationships. An invasion of even one of these relationships cannot be allowed because that would mean the destruction of all of them. Thus, each family member within the four-position foundation must guard against the possibility of love being invaded even to the point of self-sacrifice.” Family morality is therefore structural rather than merely consequentialist: any breach destabilizes the architecture of love itself.
See also. csg-four-position-foundation-is-the-ideal-of-creation