Abstract: Moral evaluation involves assessing the goodness or wrongness of actions and personal qualities. While altruism—defined as actions intended to enhance the well-being of others, often through resource allocation—is generally valued, a societal perspective posits that altruistic actions are also expected to align with prevailing social norms. This study investigates a seemingly paradoxical phenomenon: highly altruistic behavior is occasionally judged as less moral than moderately altruistic behavior. Drawing on the social functionalist perspective, we propose that observers perceive highly altruistic behavior as possessing a weaker teaching function; that is, as being less effective in guiding social life and establishing beneficial behavioral norms, consequently leading to lower moral evaluations. Furthermore, self-uncertainty, which is a negative experience stemming from doubts regarding one’s important traits or the unpredictability of the external environment, can influence social cognition and, consequently, moral evaluations. This research explores the relationship between altruistic behavior and moral evaluation, examining the mediating role of teaching function perception and the moderating role of self-uncertainty, with the aim of fostering a deeper understanding of altruism and moral evaluation to promote societal harmony.
Seven studies were conducted to test the hypothesized moderated mediation model. Initial scenario-based designs in Studies 1a (N = 272) and 1b (N = 296) explored the relationships among altruism degree, moral evaluation, and teaching function perception in monetary and temporal altruism contexts. Studies 2a (N = 313) and 2b (N = 377) employed a manipulating-of-mediating-as-a-moderator design to further test these causal relationships. Study 3 (N = 295) and Study 4 (N = 704) then examined the moderating effects of observers’ trait and state self-uncertainty, respectively. Finally, Study 5 (N = 1, 798) conducted an internal meta-analysis across all experiments, which provided robust validation of the overall model.
Consistent with our hypotheses, we present converging evidence supporting the following propositions: (1) Highly altruistic behavior, compared to moderately altruistic behavior, consistently received lower moral evaluations, both for the behavior itself and for the actor; (2) Perceived teaching function mediated the relationship between altruism degree and moral evaluation, with highly altruistic behavior diminishing the perception of teaching function and consequently reducing moral evaluation; (3) Observers’ self-uncertainty moderated the relationship between the altruism degree and perceived teaching function, such that high self-uncertainty exacerbated the perception of reduced teaching function for highly altruistic behavior, whereas low self-uncertainty attenuated this effect; (4) The internal meta-analysis substantiated the robustness of the relationships among altruism degree, perceived teaching function, and moral evaluation across both monetary and temporal altruism contexts.
Our findings offer several significant contributions to the literature: (1) The study provides novel empirical evidence supporting the societal perspective of altruism, demonstrating that moral evaluations are not only determined by altruistic intent but also shaped by social expectations, which consequently leads to lower evaluations of highly altruistic behavior; (2) The study identifies perceived teaching function as a critical mediator in the relationship between altruism degree and moral evaluation, which underscores the active role of individuals in shaping social norms through their moral judgments; (3) The study reveals the moderating role of self-uncertainty, which illustrates the dynamic interplay between individual characteristics and external social environments in shaping moral evaluations of altruism. These findings offer new avenues for understanding the complexities of altruism and moral evaluation, suggesting future research should explore these nuanced relationships across diverse contexts and behavioral domains.

Key words: altruistic behavior, moral evaluation, teaching function, self-uncertaint