"I mourn the loss of thousands of precious lives, but I will not rejoice in the death of one, not even an enemy. Returning hate for hate multiplies hate, adding deeper darkness to a night already devoid of stars. Darkness cannot drive out darkness: only light can do that. Hate cannot drive out hate: only love can do that"
— Martin Luther King Jr.
Also, most quoted by my Jewish friends and colleagues, the words of God to the excited angels who wanted to celebrate the drowned Egyptians, who had died in order that the Children of Israel might escape to freedom: "The works of my hands are drowning in the sea and you want to sing" (Talmud Megillah 10b).
An enemy is dead. This is not an occasion for singing and dancing.