Final answer:
The psychologist's claim that expressing gratitude cannot be done anonymously serves as the conclusion of the argument, emphasizing the importance of personal interactions in societal behavior reinforcement.
Step-by-step explanation:
The claim that the obligation to express gratitude cannot be fulfilled anonymously plays a specific role in the psychologist's argument. This claim is best described as the conclusion that the argument is intended to support. It is the ultimate assertion being made after considering the broader context of human psychology and the importance of personal interaction in societal behavior reinforcement.