Assuming the typical argument which follows something along these lines:
[1] Life inherently involves unavoidable suffering.
[2] Suffering is harmful, while pleasure is good; lack of suffering is good, while lack of pleasure is neutral. One cannot be deprived of experiences if they never existed in the first place, and the absence of suffering is a net positive.
[3] An individual cannot consent to being born, therefore it is immoral to bring one into a world of guaranteed suffering without their consent.
[4] To prevent suffering one must avoid procreation.
After musing about this topic for a while, following a discussion concerning it, I have concluded the theory only makes sense in the abstract, utilitarianistic sense of reducing aggregate harm; in reality, however, it is a nonsensical subversive ideology, which can be criticized on many levels; it is nonfunctional and even foolish, because as long as some individuals continue reproducing, the primary concept seems to collapse, unless you appeal to intangible potential aggregate harm.
It also leads to absurd moral conclusions about death and life, directly leading to a pro-mortalist position, and repugnant ideas such as murdering people painlessly under the pretense of harm reduction. I will admit it makes sense in theory though.