Picard's answer is shit. Terrorism is never an acceptable response.

Even in the case or violent revolutions, terrorism is a choice which typically coerces a population into submission. That will not promote a free, moral, or developed society/nation/civilization. You can't kill your way to high trust, that will literally never work and the act of murder negates any trust you build, because each person knows that they could also be killed. What you codify in such bloodshed is not a rule of law and moral arbitration among friends; but dependency among subjects, particularly to a human authority that is not a Christian God.

I'm not saying don't terrorize the enemy, or the terrorists themselves, but that's not what terrorism is. Terrorism explicitly targets the general population for political coercion. That is why even proper retaliatory violence must be done with caution, level-headedness, and fairness. The general population must feel, especially a western one, that they are governed under a fair ordering of the society with strict applications of justice.