We cannot be naturally grateful to the sources of our sexual pleasures.
The gratitude is a notion we get from education, while the pleasure lies deep in our bodily impulses. It confounds itself with the individual self consciousness.
Though it is disturbing for our social habits, it is not unnaturally that the person who feels pleasure to be hostile to those who provided her that pleasure exactly because of the gratitude for which they implicitly call. The gratitude disturbs the feeling of pleasure by altering the instrumental guise our body spontaneously attributes to those who please it.
Normally the hostility is consumed through the violence of the sexual act. Otherwise, it becomes a part of the repulsion to the persons who virtually or imaginary would be our sexual partners and generates sexist beliefs.