Each instinct and passion of man is amoral; it is only the abuse of these passions that makes them wrong. There is nothing wrong about hunger, but there is something wrong about gluttony; there is no sin in thirst, but there is a sin in drunkenness; there is nothing wrong with a man who seeks economic security, but there is something wrong with a man who is avaricious; there is nothing to be despised in knowledge, but there is something to be condemned in pride; there is nothing wrong with the flesh, but there is something wrong in the abuse of the flesh. Just as dirt is matter in the wrong place, so sin is flesh in the wrong place. Sex has its place in that area of life designed for its fruition, but the misuse of it outside of that natural and supernatural bond is wrong.
Fulton J. Sheen, Three to Get Married
sex, sin