Perversion is an ends-and-purposes disease. Most broadly understood, perversion is the turning of loyalty, energy, and desire away from God and God's project in the world: it is the diversion of construction materials for the city of God to side projects of our own, often accompanied by jerry-built ideologies that seek to justify the diversion.
Plantinga's book is filled with wonderful, descriptive illustrations of sin, its corruption, and its extent. Check it out.
Todd
