Cui bono?
Terrorism is notoriously resistant to strict definition, and the most obvious reason for this is generally understood. Unlike (for instance) guerrilla warfare, ‘terrorism’ is not merely a tactic, but an intrinsically abominated tactic. Whatever the technical usage of the word, it adheres to the register of propaganda, as a partisan denunciation. It is what the other side does.
This partisan skew is reinforced by technical considerations. Even more than guerrilla warfare, terrorism is a tactic suited to relatively disorganized non-state actors. When even guerrilla warfare is impractical, terrorism is the mode of violent ‘resistance’ that remains. In the sentimental language of the Left, it is the warfare of the weak.