Ps 137:9 Happy the one who takes and dashes your little ones against the rock!

The Psalms are known as praise songs, mostly from King David.
Most of the Psalms are encouraging, joyful, and praising to God.
They speak of deliverance, hope, and salvation.
However, Psalm 137 ends on a sour note it seems.
Who in their right mind would be happy at killing children?
Let’s run through the premise of this Psalm.
It’s definitely not from David, since it mentions sitting by the rivers of Babylon.
So someone in captivity wrote this.
The abuse of the Babylonians was so severe upon the nations they conquered, included the Hebrews, that they all hope the Babylonians would die out – become extinct.
The surest way to execute genocide is to kill the entire next generation.
You can say this is terrible (and it is) and it could never happen but since the legalization of abortion in the United States an estimated 62.5 million have died.
I wonder if those that aborted their own children are truly happy.