Ironically, women's sexual liberation leads to harems.
When women start sleeping around like men, they do choose the stable-6s that were the best they could long-term hold, they aim at one night stands with 9s. But there are only so many 9s to go around so the inevitable result is multiple women fighting over the same limited resource.
In such a scenario, women will find themselves making the logical, rational choice that its better to be in the harem of a millionaire than the sole beneficiary of a man bringing in only 50k/year. Sure, she is getting only a fraction of the millionaire's resources but that fraction is still more than all the middle class guy can offer.
In the long run, this also results in tons of males finding their access to females severely restricted. Such males are more likely to see violence as acceptable behavior when they have nothing stable that is worth protecting from violence. You get rapists, you get looters and rioters, you get militants and suicide bombers.
Women's liberation is literally the collapse of western society. The "patriarchal" system they're resisting was stable and put into place for their very benefit. But now that they've reaped its benefits, that they've only ever known its protections, they don't see a need for it so they'll pull it down, on top of their own heads.