Curses in Psalms?

"It is not the spirit of Zion but of Sinai which here speaks out of the mouth of David. This wrathful spirit is overpowered by the spirit of love. But these curses are still not on this account so many beatings of the air. There is in them a divine energy, as in the blessing and cursing of every man who is united to God, and more especially of a man whose temper of mind is such as David's. They possess the same power as the prophetical threatenings, and in this sense they are regarded in the New Testament as fulfilled in Judas Ischariot (Joh 17:12). To the generation of the time of Jesus they were a deterrent warning not to offend against the Holy One of God, and this psalm will ever be such a mirror of warning to the enemies and persecutors of Christ and his church (Ac 1:20)." (Franz Delitzsch)
"It is possible that in some of the utterances in what are called the vindictive psalms,  especially the curses in Ps 109:1-31, unholy personal zeal may have been mingled with holy zeal, as was the case seemingly with the two disciples James and John, when the Lord chided their desire for vengeance (Lu 9:54-56). But, in reality, the feeling expressed in these psalms may well be considered as virtuous anger, such as Bishop Butler explains and justifies, and such as Paul teaches in Eph 4:26: "Be ye angry, and sin not." Anger against sin and a desire that evildoers may be punished, are not opposed to the spirit of the gospel, or to that love of enemies which our Lord both enjoined and exemplified. If the emotion or its utterance were essentially sinful, how could Paul wish the enemy of Christ and the perverter of the gospel to be accursed (1Co 16:22 Ga 1:8); and especially, how could the spirit of the martyred saints in heaven call on God for vengeance (Re 6:10), and join to celebrate its final execution (Re 19:1-6)? Yea, resentment against the wicked is so far from being necessarily sinful, that we find it manifested by the Holy and Just One himself, when in the days of his flesh he looked around on his hearers "with anger, being grieved for the hardness of their hearts" (Mr 3:5); and when in "the great day of his wrath" (Re 6:17), he shall say to "all workers of iniquity" (Lu 13:27), "Depart from me, ye cursed" (Mt 25:41)." (Benjamin Davies)
"Imprecations of judgment on the wicked on the hypothesis their continued impenitence are not inconsistent with simultaneous efforts of to bring them to repentance; and Christian charity itself can do no more than labour for the sinner's conversion.  The law of holiness requires us to pray for the fires of divine retribution: the law of love to seek meanwhile to rescue the brand from the burning. The last prayer of the martyr Stephen was answered not by any general averting of doom from a guilty nation, but by the conversion of an individual persecutor to the service of God." (Joseph Francis Thrupp)
"That explanation which regards the 'enemies' as spiritual foes has a large measure of truth. It commended itself to a mind so far removed from mysticism as Arnold's. It is most valuable for devout private use of the Psalter. For, though we are come to Mount Sion, crested with the eternal calm, the opened ear can hear the thunder rolling along the peaks of Sinai. In the Gospel, the wrath of God is revealed from heaven against all ungodliness and unrighteousness. Sin is utterly hateful to God. The broad gates are flung wide open of the city that lies foursquare towards all the winds of heaven; for its ruler is divinely tolerant. But there shall in no wise enter it anything that defileth, neither whatever worketh abomination; for he is divinely intolerant too. And thus when, in public or private, we read these Psalms of imprecation, there is a lesson that comes home to us. We must read them, or dishonour God's word. Reading them, we must depart from sin, or pronounce judgment upon ourselves. Drunkenness, impurity, hatred, every known sin of flesh or spirit--these, and not mistaken men, are the worst enemies of God and of his Christ. Against these we pray in our Collects for Peace at Morning and Evening prayer--"Defend us in all assaults of our enemies, that by thee we being defended from the fear of our enemies, may pass our time in rest and quietness." These were the dark hosts which swept through the Psalmist's vision when he cried, "Let all mine enemies be ashamed and sore vexed", Ps 6:10." (William Alexander)
"I cannot forbear the following little incident that occurred the other morning at family worship. I happened to be reading one of the imprecatory psalms, and as I paused to remark, my little boy, a lad of ten years, asked with some earnestness: 'Father, do you think it right for a good man to pray for the destruction of his enemies like that?' and at the same time referred me to Christ as praying for his enemies. I paused a moment to know how to shape the reply so as to fully meet and satisfy his enquiry, and then said, 'My son, if an assassin should enter the house by night, and murder your mother, and then escape, and the sheriff and citizens were all out in pursuit, trying to catch him, would you not pray to God that they might succeed and arrest him, and that he might be brought to justice?' 'Oh, yes!' said he, 'but I never saw it so before. I did not know that that was the meaning of these Psalms.' 'Yes', said I, 'my son, the men against whom David prays were bloody men, men of falsehood and crime, enemies to the peace of society, seeking his own life, and unless they were arrested and their wicked devices defeated, many innocent persons must suffer.' The explanation perfectly satisfied his mind." (F.G. Hibbard)