When our hearts get captivated by the shiny but empty substitutes for God's way that the world offers, we miss out on the good and beautiful life that God intends.  Perhaps that is never more true than it is with the vice of lust.  Lust promises so much, but in the end, it wreaks havoc on our minds, our relationships, and our sense of personal wholeness.  This is why Jesus spoke to it so directly - so that can get free from its vice-grip-like hold on us.