Certainly a strong argument against having a child is it makes it easier for society to deal with climate change. Halving the global population has the same effect on climate as doubling the size of the Earth's atmosphere, allowing it to absorb twice as much CO2 for the same effect on climate. But if people who care enough about society to respond to an argument like this actually do respond to this argument, then the next generation will not include their children, so it will be more selfish than the current generation.
Some people believe that the main impediment to drastically reducing or stopping society's use of fossil fuels is stubborn refusal to see the light by consumers, voters and people in power. Obviously if that is the actual situation we are in, then reducing the human population will not be needed to deal with climate change. But there's a good chance that that is not the situation we are in and that the only way we can stop burning fossil fuels is to suffer a severe drop in the global standard of living if we maintain current global population levels.
Halving the global population has the same effect on climate as doubling the size of the Earth's atmosphere
assuming economics (CO2 emission) scales linearly with population.
(alt idea) I think a large contributor to greenhouse gases is transport to remote areas, so solving problems with housing prices in local areas could somewhat concentrate people and help with ecology.
There are many things to consider, many of them have high uncertainty; also people are different.
The obvious short-term consequence is that every additional child spends more of your resources and time. But even here the utilitarian ethical consequences depend on what would be the realistic alternative. For example, if your contribution mostly consists of sending 10% of your income to EA causes... then even the short-term the impact of another child might be close to zero, if you keep the same job and keep sending the same 10%. (That would assume that the money to cover the costs of the child come from some other part of your budget.)
On the other hand, if your altruistic financial contributions are more like "I only spend on myself and my family as little as I need, and send everything else to EA causes", then every cent spent on the child is taken directly from that.
How much will you spend on the child? That probably depends a lot on the child's health. A healthy baby that is breastfed and inherits stuff from older siblings... only needs diapers? A sick baby... sky is the limit.
Children consume resources and contribute to pollution, and when they become adults they also produce useful stuff. The impact of AI on all of this is also difficult to predict. Will AI cause a revolution in education? Then maybe you won't have to spend a ton of money on university. Will AI cause unemployment? Then maybe humans won't have jobs anymore, and thus your children's potential productivity will be irrelevant. Depending on when exactly the AI comes, your child might be a part of the revolution.
Second-order effects... will having more children make you happier about your life, and therefore maybe more productive or more altruistic? Will your personal example (including the decisions you made about your family) inspire other people to also become effective altruists? Again, difficult to predict. Sometimes people are inspired by their family needs to take a better-paying job; so even your future income is not necessarily fixed. Your children may or may not become effective altruists themselves.
IMHO, too much uncertainty here.
There are many variants on utilitarian theories, each with very different answers. Even aside from that though, it can really only be answered by knowing at least some definite information about the aggregated utility functions of every ethically relevant entity, including your potential children and others.
Utilitarianism is not in general a practical decision theory. It states what general form ethical actions should take, but is unhelpfully silent on what actual decisions meet those criteria.
I have one child and do not want more, so I am not seeking for personal advice here. But I am interested in the general ethical question: From an effective utilitarian viewpoint, what are the arguments for and against having children? And if we do chooose to have children, what are the arguments for having few vs. many?
I am restricting the question to rich countries. People in poor countries might face a very different set of problems.
I am not talking about generalized pro-natalism or anti-natalism. I am talking about the cost-benefit analysis. Creating more humans has a certain obvious utility in itself (if we reject generalized anti-natalism), in that it means more humans will be able to enjoy being alive. But it has drawbacks as well. Each citizen in a rich country causes an awful lot of pollution, which may accelerate all sorts of environmental disasters.
There is the concern that an aging population will put more pressure on those people of working age. It is unclear to me how this trend will interact with growing automation, and whether this problem can be fixed or merely postponed.
Furthermore, it obviously makes a huge difference whether we expect an impending singularity, an impending environmental collapse, or both.
In your opinion, is it - as a guideline - good to have many children, or is it better to have few? Why?