I think this misses the main issue.

Whether and to what extent the decision of the average couple to have children makes the climate problem worse, depends on large-scale issues of policy and technology.

If we make the large-scale shift to solar, wind, and so on that we need, probably investments in carbon capture technology as well, it will be fine for people to continue having kids. If we don’t make those changes, well, whether you’re 1 meter under water or 50, you’re still drowning.

This is a problem that demands a large-scale, systematic solution. Talking about whether Joe and Jane should or shouldn’t have kids is a distraction.

I don't personally think it's helpful or appropriate to try to discourage people from having children they want. From a population perspective, it makes much more sense to focus on preventing unwanted pregnancies, because there are an awful lot of those, especially in the U.S., where our individual footprints are especially high.

Preventing unwanted pregnancies is a cost-effective and ethical way to reduce environmental destruction and minimize population growth, and 45% of pregnancies in the U.S. are unintended. Of those, 58% will result in birth. Comprehensive sex education would go a long way, too, and many states do not include it in their curricula, even though comprehensive sex education has strong bipartisan support among likely American voters. Many women at high risk of unintended pregnancy are unaware of long-acting reversible contraceptive options, and many men don't know how to use a condom properly, which does actually make a huge difference. Besides that, it could help to ensure everyone has access to effective contraception, so consider advocating policies that improve accessibility of long-acting reversible contraceptives and help get the word out that it is ethical to give young, single, childless women surgical sterilization if that is what they want.

As for the rest of the world, it would help to donate to girls' education, since educated girls tend to grow into women who choose smaller families.

All that said, population is not the most significant cause of climate change -- it's the market failure. That's why the single most impactful climate mitigation policy is a price on carbon, and the most impact you as an individual can have is to volunteer to create the political will to get it passed.

Policy changes absolutely dwarf the magnitude of the impact of having one less child.. Let's each do our part.

No meaningful impact is going to come from whether people decide to have children or not. As someone else already previously said on this post, the changes have to be systemic, driven on the government,corporate and industrial scale.

The world population has been in decline and will likely continue to do so. Why speak of some alarmist anti-natalist, eco-fascist position when we should be holding corporations and capitalism at fault for most of this?

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Ultimately, if every action can be justified as moral, which I kind of reject as it just blows up ethics entirely, I'm not sure why they don't argue that throwing yourself off a bridge is, in fact, a net win for the environment. That not only ensures you do not reproduce, here stated as a net win, but you also stop polluting too, and probably feed some sort of aquatic life in the process.

Part of the answer is because not throwing yourself off a bridge is at least comparably moral. Alternatively, having children and teaching them to be good stewards of the earth imbues them with a much higher chance of actually cleaning the place up a bit as compared to said children not existing.