3 ideas
Keep a society's material and cultural setting fixed and swap which gender is secluded, and the stated reasons for seclusion stop making sense. Confining men 'for public safety' because they are the ones who commit violence shows that the rule was about power all along, not protection or nature. Flipping a single variable makes an accepted custom look arbitrary without any need to argue against it directly.
When women were kept out of learning and public life, Ladyland lost the scientific ability that later saved it from invasion and fed its people. The story argues that confining women is not a private domestic arrangement but a collective cost, because it takes minds out of the problems the whole society faces.
Ladyland's women collect sunlight to cook and pull water from the atmosphere to control rain, which removes drudgery, smoke, and scarcity. The utopia works through technology aimed at care and sufficiency, not through conquest.