On a global scale, the demographic transition means most nations don't care about population caps much. On a local scale, individuals won't find it cheaper to raise children in colonies; in fact the cost of life will be much higher than on Earth at first.
Of course if you're a population ethicist, then you want to increase the population and space colonization looks good.
the demographic transition means most nations don't care about population caps much.
You are taking trends that have lasted a century at most, and extrapolating them thousands of years into the future. As long as the trait "wanting to have many children even while wealthy and educated" is even slightly heritable, not necessarily even genetic, then that trait will spread, leading to a reversal of the demographic "transition".
r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.