Witness intimidation in criminal cases usually calls to mind organized-crime bosses trying to conceal their guilt. In campus Title IX proceedings, however, a different kind of mob exacts a social and professional price from witnesses who defend the accused.

Ask Tanaya Devi, a Harvard doctoral candidate in economics. Her mentor, Roland Fryer, founded Harvard’s EdLabs, which describes itself as “an education research and development laboratory devoted to closing the racial achievement gap.” Last year two unnamed women who once...