First of all we should recognize this man and his followers for what they are. They aren't just terrorists. They aren't insurgents. They are blasphemers.
What is blasphemy? The Catechism describes it thus:
Blasphemy...consists in uttering against God - inwardly or outwardly - words of hatred, reproach, or defiance; in speaking ill of God; in failing in respect toward him in one's speech; in misusing God's name. .... It is also blasphemous to make use of God's name to cover up criminal practices, to reduce peoples to servitude, to torture persons or put them to death. The misuse of God's name to commit a crime can provoke others to repudiate religion. (paragraph 2148. Emphasis added).
And scripture describes it so:
“You shall not take the name of the Lord your God in vain, for the Lord will not leave him unpunished who takes His name in vain." (Exodus 20:7)
I have little doubt that it's okay to rejoice that the punishment has taken place in this world. I have no doubt the punishment will continue in the next.
