If you wanted to bypass the intelligentsia and the church, remain undetectable to the military system, leave undisturbed the political and administrative levels of a society, and at the same time implant deep within that society far-reaching doubts concerning its basic philosophical tenets, this is exactly how you would have to act.
Effective while being tactically transcendent and evasive:
At the same time, of course, such a process would have to provide its own explanation to make ultimate detection impossible. In other words, it would have to project an image just beyond the belief structure of the target society. It would have to disturb and reassure at the same time, exploiting both the gullibility of the zealots and the narrow-mindedness of the debunkers. This is exactly what the UFO phenomenon does.