Final answer:
Functionalism is the theory that argues traditional gender roles are beneficial to society, as they contribute to its stability and functioning.
Step-by-step explanation:
The theory that might argue it is beneficial for society when men and women stick to their 'normal' roles is Functionalism. Functionalists view society as a complex system whose parts work together to promote solidarity and stability.
They assert that societal norms and institutions, such as family structure and traditional gender roles, exist because they serve a function for the larger society, contributing to its overall operation and stability. In this view, 'normal' roles for men and women are seen as beneficial because they fulfill necessary functions. For example, traditional roles might dictate that men take on the role of breadwinner, while women may focus on child-rearing and homemaking, which functionalists would argue contributes to the stability of the family unit and, by extension, society.