The thing which scares people more than anything else is not the simplest or most obvious fact that is the existential self-negation of personal (or even civilisation) death so much as it is the deeper and more profound discovery that there is an irreducible absence of meaning.
This is why people so vigorously attach themselves, as though lashed to the mast, to just about any system of belief or ideology that they happen by accident (or purely contingent enculturation of time and place) to encounter.
The greatest horror for them is not the loss of Self or personal meaning that mortality quite comprehensively represents so much as to discover that all of their reflexively self-defining purposes and values are not grounded upon anything at all.
Much might be said of the profound freedom and personal catharsis that accompanies just such a revelation of the actual and underlying groundless vacuum of meaning (or existence) that is a persistent presence of ontological absence in logic and life.
All signs point to things that need not exist but under analysis it becomes clear that signs only ever point to other signs, all definitions to other definitions and all without foundational substance or actual meaning.
In this way, meaning is only ever tautological, ambiguous and hollow; a circularly introspective and hyper-inflating labyrinth of introspective systemic pointers, references and labels.
Meaning does not exist in any ultimate sense and this entails, quite counter-intuitively, that neither do you.
That is what scares people the most: not that they themselves will one day cease to exist but that nothing beyond the tangled chaos and confusion of meaningless symbols and pointless living ever did exist.