There's a lot wrong with the argument; he has no actual justification for assuming that social science is anything like swan-spotting.
But even within his unjustified analogy... apparently if someone reports a new color of swan in Australia, he might give polygraphs and vision tests to the reporter, but sending an expedition to Australia to check it out would be of no scientific value.
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.