Saying “it’s good to be alive” is not the same as saying people have a moral imperative to bring children into the world. It would probably improve human welfare if I gave all my assets to the poor and starved to death, but I don’t have a moral imperative to do it. Judgments of overall welfare are ways of deciding what to do collectively, but no individual has an absolute duty to maximize overall welfare at the expense of his own basic desires and life choices.
(This is my personal view, not especially carefully thought-out. Some people probably do think we have an absolute duty to maximize welfare. I think your example of having to have 10 children is a reductio ad absurdum of that view, not of the view that the marginal extra human life is a good thing.)
Saying “it’s good to be alive” is not the same as saying people have a moral imperative to bring children into the world. It would probably improve human welfare if I gave all my assets to the poor and starved to death, but I don’t have a moral imperative to do it. Judgments of overall welfare are ways of deciding what to do collectively, but no individual has an absolute duty to maximize overall welfare at the expense of his own basic desires and life choices.
(This is my personal view, not especially carefully thought-out. Some people probably do think we have an absolute duty to maximize welfare. I think your example of having to have 10 children is a reductio ad absurdum of that view, not of the view that the marginal extra human life is a good thing.)