Every Christian loves the Psalms. Mostly. The oft-memorized Psalm 23 is comforting and speaks of the Lord's mercy. Psalm 150 evokes the jubilant sound of joyous musicians praising God.
And we love these happy Psalms. They're great.
It's just those imprecatory ones that many feel are....less great. Not that any part of Scripture is bad -- all Scripture is the divinely-inspired, inerrant Word of God. We just tend to squirm a little more when we read of God "[taking] up the spear and the javelin" against "the wicked." We are uncomfortable with the verbalization of a rejoicing in God's wrath.
I think it's because we're reading them incorrectly. Let's look at Psalm 68, which in the ESV is given the heading "God shall scatter His enemies" (so, y'know, friendly stuff).
God shall arise, his enemies shall be scattered; and those who hate him shall flee before him! As smoke is driven away, so you shall drive them away; as wax melts before fire, so the wicked shall perish before God! But the righteous shall be glad; they shall exult before God; they shall be jubilant with joy!
Normally, we read this and see talk of God's enemies scattered, fleeing before him, driven away "as smoke is driven away". "So the wicked shall perish before God," declares the Psalmist.
And that's all true -- it's right there in the text. But there's that second part we seem to skim right over:
But the righteous shall be glad; they shall exult before God; they shall be jubliant with joy!
This passage is a view into the Gospel. It's not some angry Hebrew poet dreaming of a day of triumph over his enemies (though probably the psalmist in question here -- King David -- was hoping for vindication from God).
It's a simple statement about reality. God will triumph over His enemies. But He also will make "the righteous" glad and "jubliant with joy."
So who're "the righteous"? All those who through Christ have been accounted as such. We, once members of the "melting like wax" group, have been brought by grace into the jubilant celebration. In three verses, we see both the destruction that we've been saved from and the victory we've been saved into.
No human can possibly be righteous unless Christ intercedes. There is none righteous, and all of us in sin deserve to melt "as wax...before fire". So for there to be any mention of "the righteous" being made glad, it can only be an affirmation of divine mercy towards those God has chosen to pardon.
Psalm 68 -- and other imprecatory Psalms like it -- may not be "He makes me lie down in green pastures", but it's no less joyful for God's elect.