I find this German revisionist history deplorable but understandable. The high percentage of people who believe the US gov. was culpable in 911, In my mind many of these people are probably actually directly culpable in WW2. The Germans of that era are Grandparents probably retired with some time on their hands and a deep seated need to absolve themselves of guilt. What would you do in their circumstance? I can't really tell what I would do.
I see a parallel in America in our relations with blacks. Some white people are overwhelmed with guilt (misplaced in my view) for the slavery and civil rights violations of the early 20th century. Thus we have spawned Micheal Moore and his ilk. If you ran a survey I am sure at least 20% of white people would report some amount of hostility toward blacks (completely unreasoned and caused by unassimilate guilt for past injustices).
The same is true of blacks in America. Some percentage of blacks feel they are intitled to special treatment because of something that happened to their ancestors. This is not based in reality either. The facts are people of any color are so monumentally better off for their being in America that it eclipses how they got here. Compare a black Americans life to a native Africans, and they are lightyears better off. Yet still the guilt remains. Coloring peoples view.
I don't think much of the conspiracy theorist and the amount of books that are sold. If you go by count of books sold in America some 20% probably believe our greatest war in the future will be with hostile space aliens from Alpha Centari. By the way there's a market for people who believe the CIA killed Kennedy. Ask Oliver Stone.