A benefit is something that improves the welfare of an entity. Prior to
its existence, there is no entity and thus no welfare, so coming into
existence cannot improve an entity's welfare.

We do not "give the gift of life" to livestock animals by breeding them
into existence; we do not do them any "favor". We facilitate their
existence, but that existence is not a gift or benefit to them. No
matter how pleasant their lives might be once they do exist, existence
itself is not a benefit to them.

No harm would be inflicted on any animals if, suddenly and for whatever
reason, we were to stop breeding livestock animals into existence. The
fact that "billions of farm animals" would thereby never exist would
have no moral meaning to any animals. There would not be any lack of
consideration shown.