A fundamental question in legal theory concerns which behaviors should be criminalized. Traditionally, this decision is seen as a deliberative process based on reason and legal principles like the harm principle. However, moral psychology highlights the role of affective and emotional processes in moral decision-making, often occurring unconsciously and leading to rationalization. While the influence of emotion on moral judgments has been extensively studied, its role in criminalization decisions remains largely unexplored. This study empirically investigates the relationship between disgust sensitivity (a dispositional proneness to experience disgust) and criminalization decisions, using virtual child pornography as a case study. Virtual child pornography is a contentious issue with varying arguments for and against criminalization, ranging from the harm principle to legal moralism. The existing debate often centers on the alleged harmfulness of such material, yet evidence regarding its direct or indirect harm to children remains inconclusive. This study posits that the decision to criminalize may not primarily stem from deliberative reasoning but rather be influenced by emotional processes like disgust, particularly given the sensitive nature of the subject matter. The study aims to correlate disgust sensitivity with criminalization decisions and theoretically proposes the development of a new perspective on criminalization incorporating a potential "criminalization bias."

The literature review extensively explores the role of disgust in moral judgment and decision-making. Evidence suggests affective and emotional processes, such as disgust, anger, and fear, are relevant to moral judgments, sometimes without conscious awareness, leading to rationalization. While various models exist—describing these processes in terms of distinct emotions, constructed emotions based on active inference, heuristics, or model-free reinforcement algorithms—the study focuses on disgust sensitivity as a measurable indicator of emotional influence on moral decisions. A considerable body of research indicates an association between disgust sensitivity and moral condemnation, particularly for purity-related violations. Individuals higher in disgust sensitivity tend to judge morally deviant behavior more harshly, especially concerning purity-related offenses, although this association is less pronounced outside this domain. However, sensitivity to other affective states also predicts evaluative judgment extremity, suggesting a broader relationship between affective processes and moral evaluation. This association between disgust and moral condemnation makes it plausible to expect a similar association between disgust and criminalization decisions. Although theoretical discussions exist about the role of emotions in criminalization, empirical studies remain limited, prompting this research.

This study employed an online survey (N=1402) using a 2 (harm: high vs. low) × 2 (disgustingness: high vs. low) within-participant design with disgust sensitivity as a between-participant continuous variable. After excluding participants under 16 and those who did not rate the vignettes, the final sample consisted of 1402 participants (517 males, 876 females, 9 unreported). A subset of 103 participants with legal expertise served as the "expert" group, matched with the lay group in terms of age and gender. Four vignettes were created: (1) wearing a clashing sweater (low harm, low disgust), (2) high-risk financial instruments (high harm, low disgust), (3) virtual child pornography (low harm, high disgust), and (4) actual child pornography (high harm, high disgust). Participants rated their agreement with the statement that each behavior should be a criminal offense on a 7-point Likert scale and responded with a binary (yes/no) decision. The Dutch version of the 25-item Disgust Scale-Revised (DS-R-NL) measured individual disgust sensitivity. Linear mixed-effects models and mixed-effects logistic regression models analyzed the data, accounting for random intercepts and slopes to address individual differences. The vignettes were presented in randomized order to mitigate carryover effects. Simulation-based power analyses determined the sample size's adequacy to detect the focal effects. Ethical approval was obtained, and participants provided informed consent.

The analysis of continuous criminalization ratings showed that vignettes high in disgust or harm received higher criminalization ratings. A significant interaction effect indicated that harm increased criminalization ratings more for low-disgust vignettes than high-disgust vignettes. Similarly, disgust affected the criminalization ratings of low-harm vignettes more than high-harm vignettes. For dichotomous criminalization decisions, main effects for disgust and harm were observed, but the interaction effect was not significant. Further analysis examined the moderating role of disgust sensitivity. A significant interaction effect between vignette disgust level and disgust sensitivity emerged. This interaction was further qualified by a three-way interaction between disgust level, harm level, and disgust sensitivity. Disgust sensitivity affected criminalization ratings for the low-disgust, high-harm vignette and, more strongly, for the low-harm, high-disgust vignette (virtual child pornography). Simulation-based power analyses confirmed the sample size was sufficient to detect the effect of interest. The model fitted to dichotomous decisions showed a main effect of disgust sensitivity, and an interaction effect between vignette harm level and disgust sensitivity. A more focused model focusing on high-harm/low-disgust and low-harm/high-disgust vignettes revealed that disgust sensitivity was more strongly associated with the criminalization tendencies toward virtual child pornography. Finally, the analysis of the moderating effect of expertise on continuous ratings revealed a significant two-way interaction between vignette harm level and expertise, further qualified by a three-way interaction between vignette disgust and harm levels, and expertise. Laypeople criminalized high-harm/low-disgust vignettes more than experts.

The findings offer preliminary empirical insight into the association between disgust and criminalization decisions. The tendency to criminalize highly disgusting behaviors, even if low in harm (e.g., virtual child pornography), contrasts with the expectation that highly harmful behaviors would be criminalized more readily. This observation challenges the assumed dominance of the harm principle in criminalization decisions. The moderating role of disgust sensitivity indicates that individuals with higher disgust sensitivity are more inclined to criminalize behaviors, particularly virtual child pornography, aligning with previous research on disgust and purity-related moral judgments. The finding that disgust sensitivity is associated with criminalization of even abstract, non-visceral behavior like high-risk financial dealings highlights the broad impact of affective processes. Legal expertise did not consistently mitigate the influence of disgust sensitivity on criminalization decisions, suggesting that professional judgment may not fully override emotional responses. This challenges the notion that legal professionals consistently base their judgments solely on rational deliberation, aligning with research on motivated reasoning which shows that legal training may strengthen rather than mitigate the effect of emotions on decision making.

This study provides preliminary evidence that emotion, particularly disgust, plays a significant role in criminalization decisions, even among legal professionals. This challenges the traditional view that criminalization is solely based on rational deliberation guided by the harm principle. The finding of a potential "criminalization bias" suggests that our emotional responses may lead to biased evaluations of harmfulness, particularly for "modern" offenses unfamiliar to our evolved moral intuitions. This study highlights the importance of interdisciplinary approaches to criminalization theory, integrating empirical data from cognitive science and philosophy of law to understand the complex dynamics of legal decision-making. Future research should investigate the broader influence of various emotions and explore the "criminalization bias" more rigorously with diverse behavioral scenarios and larger samples of legal experts.

The study has several limitations. The vignettes, while chosen for ecological validity, varied in complexity, potentially introducing confounds. Future research should employ standardized vignettes. The focus on disgust as a proxy for emotion neglects other affective processes that may contribute to criminalization decisions. The relatively small size of the legal expert group limits the robustness of findings regarding the moderating effects of expertise. Finally, using only one vignette per harm/disgust manipulation limits the generalizability of findings to other behaviors. Future studies should address these limitations through more rigorous methodological approaches.