Thanks for sharing your thoughts on this issue. While I agree that we should avoid viewing humans purely as consumers (as this is reductive and myopic), this doesn't mean our role as consumers isn't morally relevant.
You brought up the example of the speaker eating chicken and that not excluding him as a moral person. I completely agree. But no matter how many good things you do or how virtuous you are as a person, this doesn't eradicate the immorality of a separate action, such as the consumption of animal products. This is not to say eating meat makes you immoral, as the morality of a person is complex and multifaceted, but many arguments can still be made as to why eating meat, as an action, is morally unjustifiable.
I feel the same applies here with having children. We are not just consumers, but we are still consumers, and as autonomous consumers, we have choices, some of which have more harmful consequences than others. In reading this, I had the sense you find viewing humans as consumers as unpalatable, but I'm not convinced that we should stop viewing people in this way, at least in certain contexts, such as in moral discussions.
In the case of having children, it seems clear to me that procreation entails much greater environmental harm than non-procreation (which may still include adoption). You say avoiding procreation for this reason is “intuitively absurd”, but it doesn’t seem that way to me. It would be intuitively absurd if it was obvious that procreation (over non-procreation/adoption) entails overwhelming benefits to the child, parents, and world at large, but is that the case?
You also say: “To bring another life into the world is a serious ethical decision, but the impact of a new life on your life or on its own is not possible to predict in any meaningful sense.” But the opposite seems to be hold true. Suffering is the norm. The First Noble Truth of Buddhism states this clearly. If there’s anything we can predict meaningfully about a new person brought into the world, it’s that they will suffer and inevitably pass away, which is itself a harm (since most of us fear death and don’t wish to die). Other serious physical and psychological harms are regular enough to be expected in any individual’s life, no matter how comfortable it may be.
I think in these discussions, it can be more helpful to talk about whether procreation is consistent with environmentalism, rather than try to out individuals as moral hypocrites, as the latter can cause people to disengage, and it’s not always productive. Nonetheless, I see a similarity between expressing compassion for animals and eating them, and expressing environmental concerns and procreating. True, you can eat animals and treat animals well when you encounter them, just as you can have children yet avoid red meat for environmental reasons. But if we are talking about specific actions, I think a strong case can be made as to why procreation (at least in the current state of overpopulation and resource consumption) is inconsistent with an environmental ethic.