In a twisted sense, uncivilised terrorists are probably more 'merciful' when compared to civilised terrorists.

The former tend to kill their victims fast, while the latter enjoy dragging their victims through the mud, hanging them out to dry and taking great personal pleasures in prolonging their victims' pain and misery for as long as possible.

To quote an old 'civilised' terrorist :

"I'll tell you why. WE are in charge. Every government ministry and department is under our control. And in the infighting, he will go down for the count every time... I will make him crawl on his bended knees, and beg for mercy." ~ The Leech King