Final answer:
Michel Foucault argued that the simultaneous disappearance of friendship as a social institution and the problematization of homosexuality are part of the same process of societal control over sexuality.
Step-by-step explanation:
The philosopher who argued that the disappearance of friendship as a social institution, and the declaration of homosexuality as a social/political/medical problem, are the same process was Michel Foucault. In his work, Foucault explored the relationship between power, knowledge, and sexuality, focusing on how societal institutions control and define sexuality. Other prominent figures in sociology and philosophy, such as Karl Marx and Émile Durkheim, also discussed societal structures and changes, but within different contexts. Marx, for example, argued that the history of society was one of class struggle, while Durkheim's ideas were notably functionalist, focusing on social solidarity and its role in maintaining social order.