In the ethical thought of such existentialist writers as Sartre and Heidegger, abandonment is the awareness that there are no external sources of moral authority. No deity, for example, provides us with guidance or direction; we achieve an authentic life by depending only on ourselves.
(Via Philosophical Dictionary)
One inevitable consequence of this approach to morality is well described by Aldous Huxley, author of Brave New World.
For myself as, no doubt, for most of my contemporaries, the philosophy of meaninglessness was essentially an instrument of liberation. The liberation we desired was simultaneously liberation from a certain political and economic system and liberation from a certain system of morality. We objected to the morality because it interfered with our sexual freedom.
Aldous Huxley, Ends and Means: An Inquiry into the Nature of Ideals and into the Methods Employed for Their Realization (New York: Harper & Bros., 1937), 316.
It turns out to be convenient in many cases that life has no ultimate meaning: It’s the ideal excuse to fashion a morality that suits one’s individual whims. Objective meaning and purpose can prevent one from doing things one is inclined to do. As a result, such things are ignored, attacked, or reinterpreted. But they never quite go away.