Most people strictly adhere to moral rules—such as “thou shall not kill”—even when breaking them leads to a better outcome, such as sacrificing one person to save five. Is it just a bug in our ethical processing? New research points to one function of such rule following: we are more likely to trust those who abide by simple principles.

In philosophical terminology, maximizing outcomes is called utilitarian, whereas prioritizing rights and duties is deontological. A 2013 paper in Cognition revealed that even when people claim it is moral to, say, throw a dying man overboard to keep a life raft afloat—a utilitarian act—they view someone who does such a thing as lacking empathy and integrity. Now a paper in the June issue of the Journal of Experimental Psychology: General measures people's actual behavior toward those who make such utilitarian decisions.

In several experiments, psychologists Jim Everett and Molly Crockett, both at the University of Oxford, and David Pizarro of Cornell University asked American adults to respond to moral dilemmas and then interact with other supposed respondents online. When those respondents said they would push a fat man off a footbridge to block a trolley from killing five rail workers, participants rated them as less moral and trustworthy, and they entrusted them with less money in an investment game.

We don't evaluate others based on their philosophical ideologies per se, Pizarro says. Rather we look at how others' moral decisions “express the kind of motives, commitments and emotions we want people to have.” Coolheaded calculation has its benefits, but we want our friends to at least flinch before personally harming others. Indeed, people in the study who had argued for pushing the man were trusted more when they claimed that the decision was difficult.

Politicians and executives should pay heed. Leading requires making hard trade-offs—is a war or a cut in employee benefits worth the pain it inflicts? According to Pizarro, “you want your leader to genuinely have or at least be really good at displaying the right kinds of emotions when they're talking about that decision, to show that they didn't arrive at it callously.” Calmly weighing costs and benefits may do the most good for the most people, but it can also be a good way to lose friends.