Those who voice their concern against injustice are driven by reason and not emotion, research has found.
The new study used brain scans to analyse the thought processes of people with high "justice sensitivity".
"Individuals who are sensitive to justice and fairness do not seem to be emotionally driven. Rather, they are cognitively driven," said Jean Decety, a professor at University of Chicago.
Using a functional magnetic resonance imaging (fMRI) brain-scanning device, the team studied what happened in the participants' brains as they judged videos depicting behaviour that was morally good or bad.
For example, they saw a person put money in a beggar's cup or kick the beggar's cup away.
The participants were asked to rate on a scale how much they would blame or praise the actor seen in the video.
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People in the study also completed questionnaires that assessed cognitive and emotional empathy as well as their justice sensitivity.
As expected, study participants who scored high on the justice sensitivity questionnaire assigned significantly more blame when they were evaluating scenes of harm, Decety noted.
They also registered more praise for scenes showing a person helping another individual.
But the brain imaging also yielded surprises.
During the behaviour-evaluation exercise, people with high justice sensitivity showed more activity than average participants in parts of the brain associated with higher-order cognition.
Brain areas commonly linked with emotional processing were not affected, the study found.
The study appeared in The Journal of Neuroscience.