One could analyze peaceful political movements based on their stated original goals, ignore all results that only partially meet those goals, and conclude that the vast majority are hardly more effective than terrorism.

Not to mention the fact that "terrorism" itself is a propaganda term. No organisation calls itself "terrorist", and it is used to label a broad range of tactics. There are plenty of terrorist organisations that have never killed anyone or never targeted innocent civilians.

This focuses completely on the most extreme forms of terrorism, the islamic extremists with their suicide attacks. A form of terrorism that has been quite rare in the West, despite all of the publicity. And one could argue that those have been quite successful so far: with only a few successful attempts, they've gotten our full, almost daily, attention for over a decade now.