Sade has a curious ability to render every aspect of sexuality suspect, so that we see how the chaste kiss of the sentimental lover differs only in degree from the vampirish love-bite that draws blood, we understand that a disinterested caress is only quantitatively different from a disinterested flogging.
Why you were born and why you are living depend entirely on what you are getting out of this world and what you are giving to it. I cannot prove that this is a balance of mathematical perfection, but my own observation of life leads me to the conclusion that there is a very real friendship, both quantitatively and qualitatively, between what you contribute and what you get out of life.