Earlier quoted context omitted.
The logical extension of this argument is that everyone on earth should be forced to have as many children as possible all the time, because - gasp - think of all the wonderful human beings that we're missing out on. In fact, all those women of childbearing age you see walking around without a baby in their womb are guilty of a certain kind of murder . Strap them down and get to work!
The parent's comment said something explicitly different. There's a very clear line: >>If you want kids, the only reason you shouldn't have them is if you aren't up to the task of raising them -- for whatever reason. As I read it, this submission is about paternity leave and associated Zuckerberg/Facebook, not whether people should have children.
1) You can't know what the world would like if person XYZ hadn't been born. It's pure science fiction. Somebody else would probably have invented the iPhone, or figured out relativity, etc. Or they wouldn't have. There's no reasonable argument to be made here. The world would be different in ways that cannot be predicted.
2) It implies that you are withholding from your fellow man by failing to reproduce more more more, because each could be the next potential Jobs, Rowling, etc.
I also think it's a little bit ugly to point at the conclusions of difficult lives and say "hey, what a good thing that was!" Maya Angelou wrote beautiful poetry, does that mean we should congratulate slavery and racism? I'd happily live in a world without Jay Z's music if it means kids don't have to grow up in housing projects with single mothers abandoned by their fathers and 12 year olds aren't shooting their brothers over stolen jewelry.