Yes it was.

I thought Charlie Hebdo was disgusting for mocking all levels of decency, personal values, and faith or religious teachings.

That being said, insulting values or religion is protected speech, as long as that protection goes both ways. I don't see athiests or Satanists advocating for freedom of religion and the public teaching of God, so what athiests and satanists teach is not protected since they would never allow Judaism, Islam, Sikhism, etc.