Those passages in the Book of Psalms refer to taking vengeance upon the enemies of God's people back then. I've copied the psalm that so many have referenced in order to show the supposed tyrannical nature of the God of the Bible.
And today, JWs believe that Jehovah is going to take vengeance upon the enemies of God's people (all non-JWs). That's what this thread is talking about. David said many times how he couldn't wait to be delivered from the mockers, his enemies, basically anyone who looked at him sideways, and he couldn't wait until Jehovah destroyed them, their wives, and their children.
JWs are biblical fundamentalists, so it shouldn't surprise anyone that they echo these distasteful sentiments of the bible writers.
I invite any who are interested to read it through and see whether it encourages the kind of wholesale slaughter in which the WT seems to take such delight.
What it says is kill all enemies of Israel. Smash their children's heads against the rocks. The bible writers said this sort of sick crap all the time. JWs are just parroting. If we're going to criticize them for being bloodthirsty, and not the book where they got their ideas, I think that makes us hypocrites.