You exist because of a fragile string of circumstances: Your parents had to meet and procreate at a particular time, and so did their parents, and so on. If any of these things had not happened, you would not be here.
But the past that produced you also produced a whole series of historical and natural calamities — the Holocaust, World War I, and slavery, for example. Very likely those calamities influenced the delicate causal chain that leads to your existence. Without them, your ancestors would not have met and had children when they did. Properly speaking, then, shouldn’t you regret your own existence, since it required these tragedies to bring it about?
University of Haifa philosopher Saul Smilansky writes: “A ‘package deal’ is involved here: those events, together with oneself; or, the absence of the historical calamity, and the absence of oneself. So, all considered, ought one to prefer never to have existed, and to regret that one exists?”
(Saul Smilansky, “Morally, Should We Prefer Never to Have Existed?”, Australasian Journal of Philosophy 91:4, 655-666.)