A Cry for Just Retribution

Is there ever a place for asking God to avenge our enemies? Often psalms of lament include the cry for God to bring calamity on the wicked who have been treacherous to either the psalmist or to those who are vulnerable and defenceless. How can we reconcile these 'imprecatory' psalms with Christ's command to love our enemies?
Are these prayers merely an expression of an unworthy desire for personal vengeance and therefore examples of how not to pray? Or are they a justifiable longing that God might bring judgment upon those who show contempt for God's mercy and who think they can get away with cruel evil and injustice with impunity. These psalms may have more relevance than we first imagined to those who have borne the brutality of evil first-hand and who are wrestling with their pain before God.