He teaches at an elite university so it's highly probably he greatly values social justice.
Either you don't read your own comments, or you classify all social justice as signaling.
In the latter case, I'm sure you'll come up with reasons why you aren't making a fully general counterargument. I would urge you to stop for a second and ask concretely what you would have thought about, say, abolitionists.
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.