Right, but it's that sort of transition from the descriptive and the prescriptive that I'm highlighting. In liberal philosophy the issue is much more subtle, but there has been a constant interchange between the descriptive and the prescriptive. So if you look at society as sovereign individuals engaged in contractual relationships with one another, that's essentially descriptive. It was intended to be descriptive. But then your model for why individuals give up some of their rights to have a state doesn't look right and the answer to that isn't to change the model but to make a prescriptive assertion: the state should be more representative of our interests. So you've gone from descriptive to prescriptive.

Likewise, with feminism: under a model that emphasises individuals in voluntary relationships, women look oppressed, so you derive the prescriptive conclusion that we should alter family law, etc. Under the traditional family-oriented model of society, it's not even clear why anyone but the head of a household should vote, since people aren't 'sovereign' individuals, they're members of an institution - the family - and they play different roles within it, and the head of the household is its representative in society. From this shift to an individualist view you can derive much of the rest of modern liberal/progressive prescriptivism. It problematises the family - the status of women and children, the fairness of inheritance (wealth, status and genetics), familial obligations, etc - and it problematises the institutions of the state.

It's a view of people magically appearing in the world fully formed, with their own interests, and they're shocked to learn that they have parents, that they have roles in society, that society has existed long before they were born and has its own traditions, values, etc. So they're encouraged to stomp their feet and say, "Why wasn't I consulted about any of this?"