The most vocal trans-exclusionary voices are, ostensibly, “feminist” ones, and anti-trans lobbying is a mainstream activity. Case in point: Ms. Parker told the podcast “Feminist Current” that she’d changed her thinking on trans women after spending time on Mumsnet, a site where parents exchange tips on toilet training and how to get their children to eat vegetables. If such a place sounds benign, consider the words of British writer Edie Miller: “Mumsnet is to British transphobia,” she wrote “what 4Chan is to American fascism.”