The attitude of the psalms and of the martyrs is that when people resist God and persist in oppressing other people, eventually God must punish them for their wrongdoing and free their victims. But such action lies in God’s hands, not in ours. We trust God to take action; and “it is an act of profound faith to entrust one’s most precious hatreds to God, knowing they will be taken seriously.” It may also be that expressing our anger to God is better than denying that it exists, and also is calculated to make it less likely that we will act in anger (perhaps on people other than those who have wronged us—even on ourselves). But this is not a point the Psalms make.
– John Goldingay, Psalms Vol. 1: 1-41 (BCOTWP), 66-67 (internal quote from Walter Brueggeman, The Message of The Psalms, 77)