A person who goes through four years of grueling college to earn a degree that lands them a six-digit salary would presumably be a positive conclusion. The person going through these four years of grueling college chose to go to college because she wanted the six digit salary. It therefore was an accomplishment and a positive end to the process. It was all worth it.
But a person who went through four years of grueling military service across seas because they were drafted by the government but left the service unscathed and with a fully-fledged retirement plan is not a positive conclusion because the person did not initially want to participate in the draft. When the person finally goes home and tells everyone it was all worth it, he does not say it because he genuinely believes this but because he's trying to look on the bright side - now he has a retirement plan and wasn't injured during service. It was not worth it.
So it stands that our ethical obligations regarding the well-being of other people requires that we have a reasonable belief that they will benefit (re: appreciate) the action on their behalf. We also need to be reasonably sure that the final outcome will be worth it for the individual, and that it won't simply be licking their wounds but actually proud and appreciative of the fact that this entire ordeal has resulted in the way it has.
How do we know when the outcome is worth the ordeal? We know when:
- The individual either has or would have agreed to go through the ordeal.
- The individual going through the ordeal wishes the ordeal to continue.
- The outcome of the ordeal is satisfying, which typically means it is long-lasting (most likely permanent) and high in intensity of good (re: pleasure).
- There is a reasonable chance that the individual will succeed in the ordeal and appreciate the outcome.
- The problems inherent in the ordeal do not leave permanent scars on the individual, physical and mental alike.
How does this pan out in regards to birth? That is to say, is the ordeal of life worth starting?
- Did the individual agree or would have agreed to go through the ordeal? This is impossible to know, since nobody exists to ask consent of or to base a rational decision off of.
- Does the individual wish to continue the ordeal? Some certainly do. But some certainly don't. And then there's the majority who don't consciously wish to continue to live but do so out of habit.
- Is the outcome of the ordeal satisfying? Depends on what you consider satisfying. The satisfaction of banal needs and desires is surely not satisfying in the accomplishment-sense. And it is surely obvious that satisfaction is temporary while disatisfaction is ever-lingering. What is the "ontological" outcome of life? Death (re: Heidegger Being-Towards-Death). Apart from death, are there any long-lasting and high-intensity outcomes of life that make up for our otherwise uncomfortable existences?
- Is there a reasonable chance that the individual will succeed in the ordeal and appreciate the outcome? If we're talking about death as the final outcome, then it's 100% guaranteed. Does someone appreciate dying? Most likely not. Is it a given that life will be worth it to every person on the deathbed? Not in the "licking their wounds" Pollyannaism but a genuine appreciation of their existence? I personally doubt it.
- Are the problems inherent to the odeal leave permanent scars on the individual? Absolutely - just look at exponentially-rising amount of suicides every year. The process of growing up means to sufficiently repress and hide the scars of childhood. People inevitably grow old and die of some kind of disease, most likely. The celebration after the battle will always involve licking our wounds and mourning the dead - the outcome of the battle is not worth the battle itself, unless something needed to be solved by the battle. But without life, there are no problems to be solved, thus no battle is necessary.
Thus birth is at best a risk imposition and at worst a zero-sum game.