Good in what sense?
Jolyon loyally sticking to his project of forcing men on women no matter how strongly the women object.
What he means, of course, is that women are trying to ban men from Hampstead women’s pond. He says it’s time to fight women who are trying to keep men out of the women’s pond. He’d love to punch them right in the face, wouldn’t he.
If all three ponds offer mixed-sex bathing, what’s the point in labeling them men’s, women’s and mixed?
The point is to affirm people’s gender identities. Duh.