I guess Mr. Tutu has understood the message from Gandhiji wrongly. Gandhiji fought injustice using non-violence. Not the other way around. If terrorists adopted non-voilence (ironic - they wouldn't be called terrorists if they do), they could have acheived their ends of justice being done. Tutu should preach the terrorists, otherwise, Gandhian values will fail and terror would succeed and will stand justified to get their ends met.
Gandhian values have too simplistic for some people to use it anyway they like.