Without a doubt, sex is a physical act, one acted upon every second of each day by a myriad of creatures. Being human, we feel this "necessity" to pare it down to some sort of Davidsonian act, an act that needs the subconscious motivations explained. But do we?
In its simplest form, two (or more) beings engage in coitus. The base desire is procreation. It is something that is encoded in all known dna from elephants to amoebas. We couple with another, and not necessarily with a differing sex, because our genetics tell us we need to do so. Even Spock had to (Star Trek bonus points).
Being advanced creatures with few peers, or so we think, should we be above base instincts? Should we deny the animal within? And if we do not, why do we not?
Kant had the idea that sex was a degradation of human nature, a "necessary evil" almost. We participated because it was our nature to do so. To follow that line, one that could avoid having sex would be a more enlightened being. Hence chastity amongst religious sectors. In a nutshell, we have sex because we can't avoid it.
Davidson would argue (and Haack as well) that our need for sexual coupling may have nothing to do at all with fulfilling sexual need, but emotional ones or even naricissistic ones. We have sex because it appeases something other than a base instinct, from boredom to dominance of another.
Person 'A' finds person 'B' attractive. A's hormones begin to work against him/her and compel one to approach B for the sole intent of coupling. B accepts because of the same hormone reaction. What follows afterwards is not part of the sexual experience. It is the act itself that matters, the one that is in question.
In its simplest form, sexual congress is the conjoining of at least 2 individuals/creatures for the sole purpose of attempting to procreate. Whether that happens or not is moot. It is the act itself that matters. And it is in that act that Davidsonian/Pessimistic arguments fall to the wayside. Procreation overrules all other base desires.
As example, one finds another attractive. A to B. A has a subconscious reaction that causes A to desire to procreate, subconscious or not. What follows has nothing to do with the act itself. A may rape B or go home an masturbate or even have sex with C while thinking of B. In the end, the desire to attempt to procreate is satisfied.
In the end, as long as the desire to procreate is satisfied objectification of others and such is an extension of that desire and one that can be parsed from it. It is a perversion or sexual diet that while dependent upon procreation, uses it only as its initial source motivation. We have initially have sex because we want to create children. What follows once the clothes are removed can be entirely different.