What can be done about the dominance of the callous hookups of Marty and Alex, especially since the majority of people don't want it or practice it?
I think Donna Freitas is correct when she argues that discussions of sex need to be framed by Catholic social teaching. This body of literature has two concepts that are particularly helpful.
First is the notion of human dignity. In Catholic social teaching, every human being has an inherent dignity. They are of "equal value" and have a relationship with God, being made in God's image and having a "capacity for God." Moreover, as every human is a social creature, respecting dignity means honoring relationships. This notion of dignity speaks against the way Marty and Alex manipulate women—through a deft text game or pretending to be "a boyfriend kind of guy"—in order to "rack up" of thirty or forty of them.
The problem, though, goes beyond quantifying people in violation of their dignity. It is that, in acting this way, they perpetuate a system that works against people and their good. Thus, the second helpful notion of Catholic social teaching is solidarity. This is the "bond of interdependence between individuals and people," it is the truth that "we are all really responsible for all," and it is the "willingness to give oneself for the good of one's neighbor, beyond any individual or particular interest." Solidarity is about a system of relationships that does not leave people out of community life, exclude them from political and economic activities, and hinder their exercise of freedom. Marty and Alex's view of sex perpetuate a system in contrast with this solidarity, marginalizing those who differ and thereby preserving their own status as "kings."
While there is more to a good spirituality of sex and there is much more that Catholic theology needs to do in order to articulate such a spirituality, Catholicism's insistence on human dignity and solidarity is a starting point. It means that sexual activity should be used neither against people's dignity nor as part of a system that penalizes those who differ from the privileged few. Instead, human dignity and solidarity point in the direction of a spirituality where sex is animated by genuine love and this intimacy helps us to better love God and neighbor.