Short post to put down some thoughts.
Religions often place emphasis on being born. In the Abrahamic religions, birth is almost always seen as a good thing. In the Eastern religions, it's not that birth is a good thing per-se but rather it's the best way to avoid being born into a lower caste, or a lower state that is further from nirvana and the release from samsara.
Evidently, all of these religions claim some kind of salvation, whether it be Heaven, nirvana, or something else. Those born are given the chance of great happiness and pleasure in whatever the afterlife brings them.
But this is a ridiculous reason to justify birth, for two reasons:
1.) Heaven, nirvana, or the like are by no means guaranteed (you could end up in Hell, or never reach nirvana, etc)
2.) The afterlife is not even known to exist.
Ethics is presumably supposed to deal with how we should act, given what we know. This plays out in a mirror two ways:
1.) Given that Hell or endless nirvana is a possibility, why take the risk and have a child?
2.) Given that the afterlife is not even known to exist, why should it be used as a reason for decision of the awesome magnitude of birth?
I've said it many times before, and I'll say it again: THERE IS NOTHING WRONG WITH NON-EXISTENCE.