Sexual perversion, according to Nagel's 1969 essay, must be defined by what it is not. And non-perverse sexual relations, according to Nagel, involve a kind of infinite recursion: each person is at once aroused by the other (experiencer), and aroused by the other's arousal about him (Experience Machine), and also aroused by the other's arousal about his arousal about him, and so on indefinitely.
While Nagel sees the recursion as the essence of non-perverse sexual relation, it seems that another factor that is present is the balance between perspectives of experiencer and Experience Machine. Two mirrors, to display an infinite hallway, must be turned toward each other just so; similarly, the perspectives of experiencer and Experience Machine must be balanced in order to give the erotic experience of infinite mutual reference.
Non-erotic relations might also be described in this way. An ideal (even by Kant's standards?) interaction would presumably involve a balanced perspective between that of an experiencing being and that of someone who is creating experiences for others, an awareness of the inside and outside perspectives - including the other's awareness of one's own inside and outside perspectives and our awareness of the other's balanced perspectives, infinitely or thereabouts.
What I suggest is that there is an imbalance - not pure or perfect, but easily detectable - between male and female perspectives, such that males seek to be (and are) more experiencers, and females seek to be (and are) more Experience Machines. More males than females are willing to have sex with an unconscious partner - but most of those who are willing would not choose unconscious sex over sex with a conscious partner. To prefer an unconscious partner is an aberration, but for a male to be willing to have sex with an unconscious person if no other sex is available is not so unusual. Similarly, the vast majority of patrons of both male and female sex workers are men. This is the case even though few men prefer sex with prostitutes to sex with an unpaid partner - sex that thereby validates their pride as a valuable Experience Machine. Both men and women desire both experiences, but there is a measurable imbalance in the orientations of men and women.