In the best of worlds, we could catch the bad guys in a net, put pink, fluffy handcuffs on them while we talk with them gently, get to know them and understand why they did what they did. Then we could hug, and we would become friends, and one day after a not too long stay in our beautiful, green and lounge-like prison resort, we would let them out in society again and they would become productive citizens.
In our world, we sometimes have to fight. Sometimes, it's better to kill the terrorists than to risk that they attack us or to risk our soldiers getting killed in an attempt of bringing them in.