His website describes his research as:
Jason employs functional neuroimaging (fMRI) and behavioral methods to study how we infer the thoughts, feelings, and opinions of others (i.e., how we mentalize) as well as how we reason about counterfactual experiences.
That doesn't seem to me like someone who focus on advancing social justice.
You should have looked at his vita for a more accurate description of his activities. If you had looked at his paper titles, some of them indicate he's not a stranger to social justice like theorizing and investigation, and likewise his funding sources, on top of Harvard's well-earned reputation: eg. "What’s in a forename?: Cue familiarity and stereotypical thinking", "Gender differences in implicit weight identity", "Deflecting negative self-relevant stereotype activation: The effects of individuation", "Me and my group:...
Jason Mitchell is [edit: has been] the John L. Loeb Associate Professor of the Social Sciences at Harvard. He has won the National Academy of Science's Troland Award as well as the Association for Psychological Science's Janet Taylor Spence Award for Transformative Early Career Contribution.
Here, he argues against the principle of replicability of experiments in science. Apparently, it's disrespectful, and presumptively wrong.
This is why we can't have social science. Not because the subject is not amenable to the scientific method -- it obviously is. People are conducting controlled experiments and other people are attempting to replicate the results. So far, so good. Rather, the problem is that at least one celebrated authority in the field hates that, and would prefer much, much more deference to authority.