People celebrate birthdays. But what's to celebrate? First, birth is not unequivocally good. Second, it is not something you brought about. It befell you. Better to celebrate some good thing that you made happen.
"It befell you."
Riders on the storm . . .
Into this house we're born, into this world we're thrown.
Thus Jim Morrison recycling Heidegger's Geworfenheit. (Sein und Zeit, 1927, sec. 38)
For all we can legitimately claim to know, however, we may have pre-natally, or rather 'pre-conceptually' chose to enter this crap storm and go for a ride. Can you rule that out with objective certainty? No more than you can rule it in with the same certainty.
As for anti-natalism, see my Anti-Natalism and Benatar categories. Here too no objective certainty either way.