1. Imprecatory psalms express evil emotions that should be suppressed or confessed as sin (C. S. Lewis, Walter Brueggemann).
2. They are utterances consonant with old covenant morality but inconsistent with new covenant ethics (Roy Zuck, J. Carl Laney, Meredith Kline).
3. Such words may be appropriately spoken only by Christ in relation to his work on the cross and only by his followers through him (James Adams, Dietrich Bonhoeffer)
Justin gives a brief but good account of why all three views are unsatisfactory and offers a better approach that takes these psalms as legitimate prayers in certain contexts, even if such contexts are more rare in contemporary North American life. I won't repeat his reasoning, but I think he's right.
I think it's worth thinking through the possibility that love and hate are simultaneously possible and in fact even good in certain contexts. We assume that love and hate are opposites, and thus love for enemies requires not hating anyone. But there are clear biblical statements of hate for people, which Justin in an earlier post explains and defends in the context of loving enemies. Augustine's way of thinking through this issue has seemed to me to be the best way to work together these two seemingly contradictory themes. Love is our obligation, always, to any human being, whether we see the person as an enemy or not. With respect to the gospel, no one is our enemy. Everyone is a person in need of repentance. At the same time, we ought to hate evil, and people can be pretty evil. Everyone is evil in some significant ways, and we ought to hate what is evil in people.
This isn't just hating actions that are bad, since actions aren't all that makes us bad. Evil is within us, worked into the very fiber of our moral thinking, our character, our hearts and minds. We ought to hate that in anyone, and that does mean hating individual people with respect to the things in them that are evil. But what is redeemable, what will still be there if the person is transformed by God's grace, is always lovable, is always worthy of love. We aren't worthy in ourselves, without God, of any love, but what remains of God's original work (and something must, or regeneration would actually produce a new person, with the original ceasing to exist) is good. What God will do in transforming someone's mind and heart is good, and that is worth seeing as deserving of love. This is so even with the worst persecutors of Christians. Consider the example of the worst of such persecutors in ancient times, Saul of Tarsus, who was so transformed.