Who Let that into God’s Prayer Book?

Reading Psalm 137 is alarming. This is how it ends:

 Daughter Babylon, doomed to destruction,
    happy is the one who repays you     according to what you have done to us.
 Happy is the one who seizes your infants  and dashes them against the rocks. (v. 8 -9, NIV) Who let that into God’s prayer book?