The living dead persons could not scare the living ones because of the fact that they bring death among the real facts.
Since they are alive in a way or another, they cannot bring forward any trace of death. The death could not mean anything else than the total absence of life and the living dead should have at least a poor form of life.
Thus, they are scary in virtue of their poor existence and that poorness is due to the absence of a daily life. Since the daily life is able to temper any resolution, desire, or feeling, the poor life of the living dead is invested by the occult lore or the experience of nightmares with an unusual force: incredible evilness, extraordinary sadness, an unquenchable desire of revenge, and so on.
In fact, any idea or ideal which is last for us by men who lived in the past instills in us the same fear as that caused by a living dead. Our defense is the common preference for living day by day without any pressure of a demanding idea or ideal, which is replaced with the simplest forms of momentary entertainment. Moreover, it seems scary to put by ourselves our life under our own ideas or ideals, because of the fear of not being like our dead ancestors, even if the momentary entertainment could not claim to be a real life.
Unconscious or not, we thus lose any chance for becoming living dead for anybody else in the future.