A poster's thread had been deleted because he posted a link to an inappropriate website (rule violation) with no content of his own. The link was to a website that purports to "debunk" biblical content. In this case the link focused on Psalm 137, verse 9.
The NIV translation is "Happy is the one who seizes your infants and dashes them against the rocks."
T'hillim / Psalms are poems and prayers primarily written by King David. They were sung in the Temple, and we still recite them in our prayer services. They are not literal (are poems ever literal)? This psalm is about the Babylonian exile and per Midrash Eicha Zuta, it was written by ירמיה / Y'rmiyahu / Jeremiah. Ibn Ezra and the Radak stated that it was authored by exiled Jews as they "sat by the rivers of Babylon" in exile. The Gemara to Gitten 57b says that David wrote it as he was aware of the prophecy regarding the Babylonian Exile... Ergo the author is unknown, but there are plenty of suggestions!
So what is the purpose of #137?
It is bemoaning the fate of being exiled and mistreated by your enemies.
"By the rivers of Babylon, there we sat, we also wept when we remembered Zion...For there our captors asked us for words of song and our tormentors [asked of us] mirth, "Sing for us of the song of Zion." "How shall we sing the song of the Lord on foreign soil?" If I forget you, O Jerusalem, may my right hand forget [its skill]..." T'hillim / Psalm 137:1 - 5.
The Jews are in exile and their captors are tormenting them.
Do you think the Jews in the Holocaust didn't wish that Hitler would die a horrible death and his family, too? Have you never heard someone exclaim "I'd rather be dead" or "I wish you were dead"?
The Judaica Press translation of T'hillim / Psalm 137:8 - 9 is
"O Daughter of Babylon, who is destined to be plundered, praiseworthy is he who repays you your recompense that you have done to us. Praiseworthy is he who will take and dash your infants against the rock."
For what you have done to us, may you be punished! May you experience even a little of the pain you've inflicted upon us!
Again -- this is a poem, not some promise that Jews will be throwing Babylonian babies against rocks."
It might interest you to know that the Nazis did just that to Jewish babies. They would dash infants against walls until their brains exploded, they would throw a baby into the air and catch it on a bayonet -- the Nazis actually did these horrible things to Jewish babies -- not even 80 years ago...
Read the psalm, the ENTIRE psalm -- then read verse 9 realizing it is discussing the horrible tortures and barbarity that other nations perpetrated against the Jewish people.
The poet is crying out in pain at the mistreatment of his people and wishes that the tables were turned and that those who torture the Jews would experience even some of the pain we have endured.
When read in context the poet is saying that those who destroyed Jerusalem will themselves be destroyed -- and that the destruction of Babylon will not be mourned by anyone due to their treatment of their victims.