Final answer:
The New Right theorists claim that the conventional nuclear family is under threat or in decline due to the changing concepts of marriage and family, cultural Marxism, and resistance to government intervention.
Step-by-step explanation:
The New Right theorists claim that the conventional nuclear family is under threat or in decline due to various reasons. One reason is the changing concepts of marriage and family in the United States, such as increasing cohabitation, same-sex partnerships, and singlehood, which challenge the traditional notion of the nuclear family. Another reason is the perception that cultural Marxism has weaponized the culture against traditional values, leading to the erosion of the nuclear family. Additionally, conflict theorists argue that the belief in a private family sphere and resistance to government intervention in family matters contribute to the decline of the conventional nuclear family.