When CS Lewis was a young adult he had been far more eager to escape pain than to achieve happiness, and he even resented the fact that he had been created without his own permission.
One advantage of the anti-Christian materialism that he clung to was its limited danger of pain. No disaster can be infinite if death ends all. And if this life becomes too painful, one can always commit suicide for an early escape.
In contrast, the horrible thing about Christianity is that it offers no such escape. It assures each many that he is going to live forever.
The Christian universe has no door marked exit.
Perhaps a man's temper or his jealousy are getting worse so slowly that in seventy years they are not very noticeable. But in a million years they would be hell itself; "in fact if Christianity is true, Hell is the precisely correct technical term for what it would be'."
Edited from CS Lewis: Mere Christian by Kathryn Ann Linskoog, 1773. Page 101.
This passage reveals how important it is to modern materialist ethics that death is regarded as annihilation, exit, escape.
The bland assurance that 'I have a right to do what I like' is only possible when death annihilates the individual.
To guard this inversion - mainstream culture has manufactured and sustained an habitual, unthinking trope that anyone who (like nearly all humans through history and still today) believes that there is something (the soul or spirit) which survives death, is engaged in 'wishful thinking'.
So powerful is that 'wishful thinking' reflex that modern Man has ceased to examine the potentially 'horrible' consequences of survival beyond death as such (and without salvation); consequences that used to be almost universally recognised.
So, it may be seen that the death-as-annihilation assumption underpins the mainstream relativistic morality of hedonism; especially in the realm of sex and sexuality.
Of course, regarding death as annihilation also renders futile all attempts to make meaning, purpose of relationships - this leads to despair (typically unconscious, and observable by the mass personal self-hatred illustrated by chosen childlessness, and the mass national self-hatred of the planned incremental self-destruction of the West.
In sum, the assumption that death is annihilation underpins both the hedonism and the despair of modern culture. Yet the assumption is far more effective at escaping pain than enabling happiness; in the sense that genuinely to contemplate all life as utterly ended by annihilation is a numbing, demotivating thing.
Distraction by surface pleasure remains possible, but not underlying happiness; short-termist self-interest remains possible, but not altruistic, long-term motivation. The modern condition in a nutshell...
Small wonder that this assumption is so aggressively defended.