I will answer this from an Old Testament perspective which quite far from modern Christianity. The plagues of Egypt in the book of Exodus were simply terrorism. Depending on whether or not you read it literally, this was terrorism by God or by Moses in the name of God. Either way, terrorism is clearly endorsed, as I believe it should be when it is the most effective tool against an evil empire.
Today modern Western culture is pure evil, as evil as any culture cursed by God in the Old Testament. It deserves to be completely wiped out. Terrorism against the West would be justified if it was effective. My main criticism against modern terrorism is that it really isn't effective unless it is associated with clear obtainable goals, and that isn't the case with the terrorism we see today. I don't care about about those who die since they are members of an evil culture. I just think the terrorism is pointless and the energy would be better spent building up positive religious movements.