There are many good Muslims out there: I can feel them. There are also many cruel ones, who derive great satisfaction from sadistic violence in the name of God. Such a God is indeed not great.
That Islam can be turned to Goodness was shown by the Sufis. If it is a Goodness which wants to be insular and left alone by the world–a partial Goodness–I am fine with that. As long as they leave me and mine alone, we can share this planet happily.
TError as a political tool has of course been used many times in history. If memory serves, it was the Chinese Qu regime that tried to destroy all learning not originating with their state, and which burned many scrolls and buried alive many scholars to accomplish this end.
In the modern world terror has been used most often and perfected by the creed which calls itself “Marxist-Leninism”. As I understand the matter, Islamic terrorism can credibly be claimed to have originated in the minds of Soviet-bloc agitators. There is nothing in the Koran to justify it, and for his part Mohammad is at pains to denounce violence between Muslims. If the House of Peace becomes a House of War, then the point of the religion vanishes.
As I see it, over the long haul the best way to curb Islamic extremism is to build and build empirical understandings of the nature of the afterlife. This is certainly possible, and in a rational culture would be the subject of tremendous and well funeded investigation. It does not fit the ideological bigotries of those who control the money, however, so it languishes.
That I am the only one I know of saying such a thing explicitly speaks volumes to the idiocy on this planet.