Just so we're clear, there is such a thing as Christian terrorism. It is just FAR less common, in MUCH smaller scale when it does happen, and FAR better policed than Islamic terrorism.
Lots of white-supremicists groups, historically the KKK, but now many smaller groups commit terrorism and maintain strong Christian-based identities.
Several Christian groups, like Army of God, have committed abortion-related terrorism, the most notable of which was Eric Rudolph's Olympic Park bombing, killing two and injuring 111. (Acts of this scale are so common in Islamic terrorism that they really aren't even very newsworthy any more, at least when they happen outside the west)
The Hutaree were found making advanced IED's (Explosively Formed Penetrators, specifically, for taking out armored vehicles)- not exactly something you use for self-defense, although they never actually committed any terrorist acts.
Overseas there is still far more pronounced Christain terrorism, like the burning of children as witchs in Africa as well as conflicts in Bosnia, not to mention the recent Catholics vs. Protestents in Ireland.