Good writing, but bad argument. Some things that make those "systems" different:
1. The market domain is much "wider" than sex. Money influences every aspect of your life.
2. The exact same argument could be made about many other "systems of differentiation". Such as skill or physical and mental health.
It's a cheap argument to make it seem like socialist arguments against economic inequality also applies to some kind of "sexual inequality". Sounds like an argument that eventually leads to Handmaidens tale, but I could just be imagining things.
Fact is that socialism isn't about removing all differences or all unfairness in the world at all cost.
It's about constructing a system that limits the negative side effects of the market economy.
One aspect of that is to avoid the commercialization of non-economic aspects of life.
What Houllebecq describes is the opposite. Love as a commodity.