Although there are many non-human species — especially — that also cause a lot of suffering, humans have the unfortunate distinction of being the mos… - David Benatar

The argument that coming into existence is always a harm can be summarized as follows: Both good and bad things happen only to those who exist. However, there is a crucial asymmetry between the good and the bad things. The absence of bad things, such as pain, is good even if there is nobody to enjoy that good, whereas the absence of good things, such as pleasure, is bad only if there is somebody who is deprived of these good things.

Human life would be vastly better if pain were fleeting and pleasure protracted; if the pleasures were much better than the pains were bad; if it were really difficult to be injured or get sick; if recovery were swift when injury or illness did befall us; and if our desires were fulfilled instantly and if they did not give way to new desires. Human life would also be immensely better if we lived for many thousands of years in good health and if we were much wiser, cleverer, and morally better than we are.

Disability rights advocates also correctly note that quality-of-life assessments differ quite markedly between those who have impairments and those who do not. Many of those without impairments tend to think that lives with impairments are not worth starting (and may even not be worth continuing) whereas many of those with impairments tend to think that lives with these impairments are worth starting (and certainly are worth continuing). There certainly does seem to be something self-serving about the dominant view. It conveniently sets the quality threshold for lives worth starting above that of the impaired but below normal human lives. But is there anything less self-serving about those with impairments setting the threshold just beneath the quality of their lives? Disability rights advocates argue that the threshold in most people’s judgements about what constitutes a minimally decent quality of life is set too high. However, the phenomenon of discrepant judgements is equally compatible with the claim that the ordinary threshold is set too low (in order that at least some of us should pass it). The view that it is set too low is exactly the judgement that we can imagine would be made by an extra-terrestrial with a charmed life, devoid of any suffering or hardship. It would look with pity on our species and see the disappointment, anguish, grief, pain, and suffering that marks every human life, and judge our existence, as we (humans without unusual impairments) judge the existence of bedridden quadriplegics, to be worse than the alternative of non-existence.