Since the 1995 publication of Daniel Goleman’s bestseller, emotional intelligence has been touted by leaders, policymakers, and educators as the solution to a wide range of social problems. If we can teach our children to manage emotions, the argument goes, we’ll have less bullying and more cooperation. If we can cultivate emotional intelligence among leaders and doctors, we’ll have more caring workplaces and more compassionate healthcare. As a result, emotional intelligence is now taught widely in secondary schools, business schools, and medical schools.

Emotional intelligence is important, but the unbridled enthusiasm has obscured a dark side. New evidence shows that when people hone their emotional skills, they become better at manipulating others. When you’re good at controlling your own emotions, you can disguise your true feelings. When you know what others are feeling, you can tug at their heartstrings and motivate them to act against their own best interests.

Social scientists have begun to document this dark side of emotional intelligence. In emerging research led by University of Cambridge professor Jochen Menges, when a leader gave an inspiring speech filled with emotion, the audience was less likely to scrutinize the message and remembered less of the content. Ironically, audience members were so moved by the speech that they claimed to recall more of it.

The authors call this the awestruck effect, but it might just as easily be described as the dumbstruck effect. One observer reflected that Hitler’s persuasive impact came from his ability to strategically express emotions—he would “tear open his heart”—and these emotions affected his followers to the point that they would “stop thinking critically and just emote.”

Leaders who master emotions can rob us of our capacities to reason. If their values are out of step with our own, the results can be devastating. New evidence suggests that when people have self-serving motives, emotional intelligence becomes a weapon for manipulating others. In a study led by the University of Toronto psychologist Stéphane Côté, university employees filled out a survey about their Machiavellian tendencies, and took a test measuring their knowledge about effective strategies for managing emotions. Then, Cote’s team assessed how often the employees deliberately undermined their colleagues. The employees who engaged in the most harmful behaviors were Machiavellians with high emotional intelligence. They used their emotional skills to demean and embarrass their peers for personal gain. In one computer company studied by Tel-Aviv University professor Gideon Kunda, a manager admitted to telling a colleague “how excited we all are with what he is doing,” but at the same time, “distancing my organization from the project,” so “when it blows up,” the company’s founder would blame the colleague.