Subjects also completed the Harm and Purity segments of the Moral Foundations Questionnaire (MFQ), a test designed by Jesse Graham, Jonathan Haidt, and colleagues to measure the degree to which people’s ethical values are based on concerns about harm, fairness, loyalty, authority, and purity. Items to be rated included “Compassion for those who are suffering is the most crucial virtue” (a measure of concern for harm) and “People should not do things that are disgusting, even if no one is harmed” (a measure of concern for purity). Then subjects rated how easily disgusted they are (by things like cockroaches and mucous) and how easily angered they are. Finally they reported their level of religiosity and political conservatism.

Unsurprisingly, the degree to which subjects thought the homicides mentioned in the obituaries were harmful reliably predicted the degree to which they thought the homicides were morally wrong. Purity did not predict wrongness. But for the suicides, the reverse was true: wrongness was predicted by ratings of purity (the suicide tainted the victim’s soul) but not harm. Similarly, concern for purity on the Moral Foundations Questionnaire predicted judgment of the suicides as wrong, but concern for harm did not; the reverse was true for homicides. Additionally, both disgust at the deaths and the degree to which subjects were easily disgusted predicted their judgments of the suicides as wrong; neither anger at the deaths nor being easily angered did. So people in the study considered suicide immoral because it disgusted them—viscerally and spiritually.

Subjects’ ratings of the suicides as harmful did exceed their ratings of the suicides as soul-tainting, but because only the soul-tainting judgment correlated with their judgments of the suicides as wrong, the authors argue that we consider suicide wrong primarily because it’s a purity violation. If we didn’t consider suicide impure, would we consider it harmful but somehow not morally wrong? Rottman says yes. He told me that of the people who gave the lowest possible ratings of soul-taint (1 on a scale of 1 to 7) on all suicide obituaries, their harm ratings averaged 5.62 out of 7, similar to the overall group average, but their wrongness ratings averaged 3.33, significantly below the midpoint on the scale (4). So those who didn’t see suicide as impure thought it was very harmful but not very wrong. (To make sense of that seeming paradox, Rottman notes other acts that some consider harmful to others but not morally wrong: eating meat, extracting teeth, executing prisoners.)

The notion that suicide is wrong because it taints the soul might sound foreign to atheists. But even when only non-religious liberals were considered (those who rated themselves below the midpoint on religious belief and political conservatism), the wrongness of the suicides was still predicted by ratings of purity and not by ratings of harm. According to Rottman, the pattern holds even among people who gave themselves the lowest possible rating on religiosity (1 of 7). Concern about the soul’s purity is not just for church-goers.