The most ancient and important taboo prohibitions are the two basic laws of totemism: not to kill the totem animal and to avoid sexual intercourse with members of the totem clan of the opposite sex.
Sigmund FreudFree sexual intercourse between young males and respectable girls" was urgently necessary or society was "doomed to fall a victim to incurable neuroses which reduce the enjoyment of life to a minimum, destroy the marriage relation and bring hereditary ruin on the whole coming generation.
Sigmund Freud