It's neither the costs nor the extrinsic carrots that make people consider whether to have kids or not. Costs are no object if you love your kids. If you have to be rewarded for having them, perhaps you aren't having them for the right reasons.
Above all else, when we become parents, we want to be the best possible parents to our kids. This means we want to provide the best possible chance of survival to our kids, and assure ourselves that our kids can grow up and live long and happy lives.
At our current level of social development, we tend to concentrate our available resources on raising one kid, or at the most two, for replacement sake. The fewer the number of kids sharing resources, the more likely the chance of survival. But that's literally putting all our genetic eggs into one (or two) baskets. The game we are playing is a gamble and the stakes are really high at the level we are playing.
The stakes are raised even higher when resources alone are not enough to secure assurance for the lives of our egg-baskets. We have artificially inflated the stakes even higher by pegging our kids' happiness and survival on personal achievement, evidenced by quality certification and documentation. Nothing less will do. Not for us, not for our kids, and certainly not for society whom we feel is beholden to us to help raise our kids, though how we arrived at this delusion is a mystery.
In a social structure like this, parental love becomes conditional. Parents love their kids when they score straight As, or their love is withheld until they do. Kids who need constant parental love are often made to feel they have to deserve it. Acceptance is gained by having to prove oneself again, and again, and again. Thus, within the household, relationships are strained all round. Given a choice, who would want to live like that?
The stakes aren't so high if you raise pets, though. General maintenance; medical expenses; treats; toys and the like are not cheap, but we spend without thought because we love our pets. Granted, they don't cost as much as raising kids, but that only makes things worse, doesn't it? The dog failed basic obedience; is probably as emo-psycho as any teenager and probably has a few undiagnosed learning disabilities as well, but hey, what the heck, right? Her future isn't dependent on stellar academic records, so we still love her just the same. She's done nothing to make us proud of her, but we still do our best to make her happy, anyway.
If we want more kids (the human kind), we have to make the C grade respectable again. My educational influences taught me that C stands for 'Competent', and that was good enough a benchmark to aim for. Achieving a C does not require kids to work unusually hard nor feel as unhealthily pressured, scared and hopeless as many kids are experiencing now. Aiming at a C allows a kid to develop interests, learn from other less academic sources and become more well-rounded as a person. By having time and space to see the world in all its horrors and wonders, a kid acquires broader perspectives and whatever knowledge is picked up in school falls into a useful context that helps make sense of the often weird and confusing things that happen around us all the time... if only we would look up from our books once in a while, busy as we are chasing an ultimately unappreciated bunch of As
But in our current society, encouraging your kid to aim for a C is the height of irresponsibility when all the other parents are making their kids score As by any means possible. This is not a game any rational person would want to play. And S'poreans are nothing if not rational.