I have found numerous examples where people reference Psalms to justify their theological positions. However, because of the unique genre and purpose of Psalms, is it acceptable to do so? If so, how do we then reconcile Psalms like psalm 137:9?
Happy is the one who seizes your infants and dashes them against the rocks.
Psalm 137:9 NIV
There are people who use this scripture in order to deny that God exists, and to deny that the Bible is God's word. But Satan is not God's judge!! Nor are people who make up problems about His word, when in fact they do not believe in God, in the first place. So, do not be afraid of how ones use this scripture to accuse and criticize God. God does not need to be protected or rescued.
Our character can effect how we see things in God's word. The Bible can discern where we are at.
Considering all which the Bible says about God and reality and love, I can see this scripture means and confirms a number of things the Bible says.
This is directed against parents who are evil. And there is "the spirit who now works in the sons of disobedience." (in Ephesians 2:2) And we have scripture to indicate that humans are born in sin. So, these evil parents, I understand, could have spread their evil spirit, at conception, into their children. And therefore this scripture shows how unsafe even infants are, if they are not of the Holy Spirit and God's love.
But Jesus came and suffered and died like He did, so we may have forgiveness and eternal life in God's own love. Jesus died on the cross with hope for any evil person, at all. I consider that Jesus suffered and died like that, because He knows how horrible it is to live in sin and how awful hell is; He considered it worthwhile to suffer and die like that so we do not go to hell; He knows how bad hell is, and He suffered that much, partly in order to make sure we do not go there. But people try to outsmart God; this is not wise, after all Jesus has done and demonstrated.
So, there can be judgment if and how God knows it is necessary, but He prefers the Jesus way.
And so, we need to have compassion for ones not of God, and do all God has us do to help them to be turned "from darkness to light, and from the power of Satan to God" (in Acts 26:18).
This scripture about smashing kids shows that evil is a reality, and that God can use severe measures to fight it. But when humans take it on their own selves to kill people, for the sake of their self-righteous justice, they can face severe consequences. It is not for humans to take justice in their own hands, or to make themselves the judges of God.
"consider the goodness and severity of God" (in Romans 11:22)
If God does decide it fits with His overall plan and purpose, that children die, He will do the right thing with each of them after they die. And it can be better in the next existence . . . or much worse. And we can not get ready, ourselves, so the next existence will be good for us. So we need to now trust in Jesus for how He is able to prepare us. Suicide, then, and mercy-killing others is not going to help. We need to live and die in obedience to God and how He rules us in His own peace > Colossians 3:15, Isaiah 58:11.
Sunlight can be good for giving life, but also the same sunlight can be very severe to a worm on the sidewalk. There is life and wrath in the same sunshine. It depends on your nature, how you are effected by God
But God is able to change your nature so you benefit from Him, in case you don't.