To be born is arguably the worst injustice, one cannot consent to being thrust into existence, for to say “I consent” implies that there is an I, that existence is already attained. It is to be, in the inverted sense, raped by mother nature, a one in a trillion rape, a one in a trillion, horrific injustice. And of course, we are wired to consent after the fact, after we already exist. “I don’t want to die” is the norm thanks to natural selection, and I say that not cynically. I say that as someone who has had depression in the past. In absolutely no way do I defend or support social Darwinism, but natural selection as opposed to human selection has hitherto been responsible for shaping our instincts and minds from birth, not to say that they are not largely malleable by the material conditions and society this mind finds itself in, but that the general trend has been a desire to live and survive, the most deeply rooted instincts.
This is also not an argument against procreation. Yes, we should have fewer babies because of overpopulation, but by all means, have children if you so will. Just know that it is as you will, or the material conditions you find yourself in (i.e. sex, rape, moral stance against abortion or contraception, etc.) and not a non-existent other, not according to the will of the thing you are going to thrust into the world without its consent. But there is a silver lining, being a good parent helps to atone for this injustice, in fac, if you are responsible for creating this thing then it is you alone, with (hopefully) the obligation of the other, that can, and therefore must do to atone for this injustice.
Perhaps this can explain the paternal/ maternal instinct. “My god I have brought this innocent thing into the world, It’s so helpless.” And then in the subconscious, “It couldn’t even consent to being thrust into existence, I have to give it a happy life and be a good parent to make up for this”, even though it is in most every regard a most happy moment. I think this may be a valid form of subconscious moral reasoning. In essence, you do not choose to exist, someone and something else did. To be born, to exist against your will is in the absolute sense, injustice. But this is an absolutely necessary, and permanent injustice. Not in the sense that immorality, oppression, and exploitation are unjust, but in another, wholly existential and absolute form.