The Diamond Sutra's double negative looks like this:
Self is an illusion, the negation of self is also an illusion
Sentient being is an illusion, the negation of sentient being is also an illusion
Dharma is an illusion, the negation of Dharma is also an illusion.
Scholars racked their minds for centuries, and most Confucius scholars gave up long ago! And so did philosophers of an analytical bend (which include most modern scholars of our philosophy department; the isolated ones who still teach metaphysics would likely interpret these double negative in more mysterious language than the Sutra itself).
Psychologists of the unconscious (in particular Carl Jung) come to the rescue. Without ego, there will be no consciousness and no personality as such. A complete domination of the ego is an illusion and lead to a revolt of one's unconscious and, according to Jung, a fast way to become neurotic. An understanding of our darker side (our shadow) is the first step to an integration of our total personality. For the psychiatrists, it is only relevant for pathological cases; for the religious leaders (in particular Zen and Tao masters), it is a possible enlightenment for each of us. Whereas the Diamond Sutra set the objective or the possibility of enlightenment, it doesn't spell out the route. Or as the Sutra says: there ain't no route (or route is an illusion, and so is the negation). And the Buddha is probably right!