I'm with Sammwich, humans are emotional, advocating allowing children to starve simply wouldn't fly.
Assuming space-living; the primary problem is scarcity of resources. You can't simply emigrate or give your child away if you have too many. If you want to restrict resources post-birth as eyaras describes, you're basically punishing children for crimes they had no part in. There's lots of legal/moral arguments against that.
Which ultimately means you'd want to prevent pregnancy from occurring or completing, either through incentives, sterilisation or abortion.
If incentives fail, there wouldn't be an alternative except for draconian measures, barring massively expensive redesigns of habitation.
In a practical sense however, I don't think we'd have to worry too much about this problem. Any spacefaring citizens would likely be rich relative to the terrestrial average, and we can see very low birthrates in rich countries. So much so, that incentives to procreate might be required.