This is a good point, because it is exactly what al Qaeda did.
When the planners originally brought the idea to bin Laden, it called for acquiring military planes and flying them into buildings, IIRC. bin Laden said, "Why make it so complicated? We've got all these airliners flying around, let's just hijack a few." This little change probably cut the complexity of the plot in half, thus greatly increasing the chances of success.
This is exactly why al Qaeda is such a successful terrorist organization; unlike the governments they are fighting, they are lean and mean. They don't have to form committees and sub-committees to argue for hours on end over which color font to use in their memorandums. They don't have to involve as many people...which is good, because one thing they apparently don't teach their operatives is how to hold up under interrogation.
Most of all, the advantage they have over their more civilized opponents is that they have no moral scruples, something truthers appear to believe is true of everyone.