Is it ethical to have biological children when there are children who could
I think you're onto a profoundly important question, and I share your concern that the issue is not commonly one encounters in public discourses. I think the issue of having children is, as you say, bound up with concerns about prioritizing existing needs and also about the environmental consequences of additional pollution, consumption, habitat loss, etc. I think the issue, however, concerns both the more developed and the less developed world. The impacts from reproduction in each are different, but those impacts in both are substantial. Currently the levels of consumption in the less developed world are low, but we can't demand that populations remain impoverished. Moreover, populations in the less developed world are despite low individual levels of consumption nevertheless collectively exerting enormous pressures on non-human populations through their effects on water, habitat, and pollution. It is clearly, then, not morally unproblematic to reproduce under current circumstances for any of us. There, are, however, countervailing imperatives and mitigating qualifications that argue in favor, at least in a moderated way, for reproduction. Countervailing imperatives include the imperative to sustain cultures, families, and institutions that would cease to exist without a replenishing rate of reproduction--both in the poorer and wealthier parts of the globe. In addition, individuals find important moral and personal excellences as well as extraordinarily deep pleasures in bearing and raising children that would be lost with a moratorium, even for a short period. The window of reproduction for individuals is extremely small in relation to the time it will take to solve the grand problems we're considering. Think of these as our duties to ourselves. Qualifying or mitigating considerations include that halting reproduction in the developed world is not by itself either necessary nor sufficient to address the needs of those who require more resources both in the developed and less developed regions of the globe. Many of the problem we face are related to problem rather than to the finitude of resources. My own view is that it is in most circumstances wrong to reproduce at more than the rate of replacement, and that the world generally should move towards measures to reduce reproduction to less than the replacement rate. I'd guess that human populations should be reduced by at least a half over time, perhaps by two thirds. You may have seen the recent recommendation of biologist E. O. Wilson that we set aside at least half of the Earth for non-human species. That seems a reasonable goal to me. We must also aim for a population that can not only exist in poverty but instead flourish without the use of fossil fuels and perhaps also without the use of nuclear power.