Rapaire, has ELF ever been responsible for death or injury to a person?
Anyway, the examples I cited (of inappropriate application of the term "terrorist" to groups like Earth First!) were not examples of arson.    (I do believe some organizations that go out of their way to avoid injury to people sometimes take too many risks that people may be hurt or killed.)
I have heard news broadcasts wherein people/groups were labeled "eco-terrorists" for doing things like lying down in front of logging trucks (classic Ghand-style passive resistance) or spray painting signs on a building (vandalism) or getting between whaling ships and whales (interference with a business enterprise). I believe the FBI classifies groups "terrorist" groups if they do such things, even if no one has ever been hurt.

In Tiller's case, I don't think the intent was simply to assassinate a person. I think it was to strike fear in the hearts of anyone who performs or assists in abortions, no matter what the circumstances.   If Operation Rescue people want to lie down in front of the entrances to "abortion clinics" or spray paint slogans on their walls, I wouldn't call that "terrorism" either.

But I think having bomb-making stuff in your house and then gunning down someone in church, while he was serving as an usher, qualifies as terrorism. I imagine that not just the other staff at Dr. Tiller's clinic but also the members of his church congregation may feel a lot of fear.