Scarlet Letters and Whited Sepulchres: The Social Making of Relationships as “Inappropriate”

For or what reasons and on what grounds is a relationship to be judged “inappropriate”? The term relational “inappropriateness” obviously suggests a contrast between appropriateness and inappropriateness of personal relationships, and that relational behavior may be judged accordingly. Why is it customary to judge personal relationships, private behavior, or intimacy as “appropriate” or “inappropriate”? What is “appropriate” behavior, “appropriate” relational behavior, or an “appropriate” relationship? Who decides?