From his perspective as an economist, Wydick considers the act of sex as a type of exchange.
"Seen in the simplest of terms, women are exchanging sex for commitment, and men are exchanging commitment for sex. Based on a male and female's basic biological needs, for males the price of sex is commitment and for women the price of commitment is sex."That's a position he leads up to rather than assumes, and he emphasises that he is not implying that women don't enjoy sex or that men do not enjoy commitment. So don't take that quote as his whole case.
Wydick draws conclusions from this position mostly for men -- which is quite appropriate given his own gender. But I can't help thinking that a female perspective on this "exchange" may be significantly different.
Anyway, he does make what I think is a good point that this "exchange" has lead to an issue of justice because the prevailing social norm over-values sex and undervalues commitment. (It strikes me that there could be an equivalent issue of justice if the reverse imbalance occurred as well, but that's perhaps not the injustice we see in modern western culture.) In that case, sex becomes "cheap" and the woman in need of commitment is ripped off.
"When a man receives sex from a woman without paying the price of commitment, he takes something for which he has not paid. Put simply, he is stealing. ... Social justice requires that men fulfill their end of the exchange."
The injustice may still occur when a woman "consents", because a wide variety of social expectations may nevertheless be acting coercively on her to force her consent.
My problem with Wydick's position is that it over-generalises on two fronts. From my personal biography, it over-generalises the gender distinction. What if one party (or both parties) value sex and commitment equally? Like many males I know, I have a deep need for connection, belonging, affirmation and for someone to stand by me for the long haul. Two people's discussions about the appropriateness of sex in their relationship can be just as often about "how can we nourish each other with both pleasure and security" as about "how much of the one must I give you in order for you to give me the other."
It also over-generalises what constitutes consent and consequently diminishes personal empowerment of choice. I agree that there is a transaction inherent in sex and there is a power dynamic in the negotiation between the two parties. That happens both within marriage as much as it does without. In a wholesome relationship there could (should?) be honest discussion about what is being exchanged and a set of shared expectations that meet both parties' needs. The needs are the not same in all cases and the relative value of physical pleasure, long term commitment and numerous other "costs" and "benefits" undermine Wydick's simple model. There may be other value in the exchange for women other than commitment, and I would prefer to fully empower a woman to make a real choice than to remove their choice by applying a generalised rule.