St. Maximos the Confessor interpreted the Psalm 137:9 lines as being about uprooting forbidden desires.

Every assent in thought to some forbidden desire, that is, every submission to self-indulgence, is a sin for a monk. For first the thought begins to darken the intellect through the passable aspect of the soul, and then the soul submits to the pleasure, not holding out in the fight. This is what is called assent, which - as has been said - is a sin. When assent persists it stimulates the passion in question. Then little by little it leads to the actual committing of the sin. This is why the prophet calls blessed those who dash the children of Babylon against the stones (cf Ps. 137: 9). People with understanding and discretion will know what is meant.

Bishop of Diokleia Kallistos; St. Makarios of Corinth. The Philokalia . Kindle Edition.