Do not rejoice when your enemies fall, and when they stumble, do not let your heart exult…
- Proverbs 24:17
Thus the LORD saved Israel on that day from the power of Egypt. When Israel saw the Egyptians lying dead on the seashore and saw the great power that the LORD had shown against Egypt, the people feared the LORD. They believed in the LORD and in Moses his servant.
Then Moses and the Israelites sang this song to the LORD…
- Exodus 14:30-15:1
Whereupon the Holy One sat in judgment over the Egyptians in accord with the measure of justice and drowned them in the sea. In that instant the ministering angels wished to utter song before the Holy One, but He rebuked them, saying, “The works of My hands are drowning in the sea, and you would utter song in My presence!”
- Midrash Avkir
The answer is somewhere in the middle of yes and no.
When the Egyptians were drowned in the waters, the angels in heaven rejoiced and were rebuked by God while the Jews rejoiced on earth and God said nothing.
The Scriptures warn us against rejoicing in the downfall of our enemies. The reason for such a warning is obvious: pride, arrogance, vengeance, etc. are not to be associated with the People of God.
In a perfect spiritual world, we would see the downfall of a grave sinner as a lost opportunity and a lost soul. Someone made in the image and likeness of God and loved by Christ turned his/her back on that love and lost so much potential for goodness and love.
However we do live and operate in a fallen world, we suffer greatly at the hands of such individuals. To rejoice that evil, suffering, fear, etc. have been conquered through justice is not a bad thing.
The morality of such rejoicing would depend on just what exactly we are rejoicing over. If we are celebrating the death of an individual with a sense of vengeance, hatred, and arrogance then we are indeed sinning.
But if we are rejoicing because of our relief that the evil and suffering has ended in this situation then we are celebrating justice, goodness and love and as such would be perfectly moral.