Hi OP, I've not read the whole thread but I was skimming it last night whilst awake with my baby. 5 months old and he's already lived through 5 heatwaves.
Both my partner and I work in the environmental sector and work with the reality of climate chaos and ecological collapse daily. We had pretty much decided not to have (biological) children and this was a huge factor in that decision, and I think it is a very respectable, reasonable choice (not at all doomerism) if you do decide not to. But here we are...
There is a massive emotional component to making the decision which can't really be rationalised but for us at least we also went through the mental gymnastics, as have many of my friends and colleagues (as others have said, lots of climate scientists do have children, although often only 1). I'll explain some of the key points that ultimately meant we decided to go ahead.
Firstly, this isn't a new problem. It is different from a war, plague, politics etc but it's not new. Many people will say "oh I feel so guilty for bring my children aged 15/ 20/ 30 into the world, I wouldn't do it now". This is bollocks that people tell themselves to try and paint themselves as climate conscious, but we've know about this issue for a long time (academically and publicly). I learnt about it in school and the predictions were more dier at that point. It's very easy to say you wouldn't have children after you've had them, but the reality is having children is always a selfish decision whatever the time and place you bring them into - own that decision. My parents knew all about environmental crisis but still had me, and my life has for many global reasons (financial crash etc) been objectively harder than theirs, but it has still up to this point been good and I don't resent being born.
Bringing a child into this world means bringing them into uncertainty and you cannot guarantee a good life, but this has always been so. However, it does not mean certain doom and misery. The world is changing and that is going to bring MASSIVE change and challenges, this can't be understated, but it does not mean the planet is going to be completely unlivable, we have the opportunity to adapt.
There are many climate and ecological changes locked in but we also have the solutions for slowing warming and adaptation. The biggest issue we face right now is political will. Every degree of warming makes a difference. What often doesn't get reported is the enormous progress we have made. We have already hugely reduced the rate of warming (when compared with what was being predicted when I was a child) because of the rapid and unexpected progress on renewables. Your carbon footprint is probably similar, if not less than that of your grandparents despite use of more days to day technology, taking more flights etc, and this is all down efficiency in technology and renewable usage. We can do better. And there will come a tipping point (soon I believe as the issue is now landing on western shores) where politicians can no longer deny the issue and there will be action on adaptation in particular.
Finally, when considering if I should have a child my colleagues who already had children advised me to think about what advice I would give to my child if they were already here. And it's this - live a big beautiful life. Do so responsibly, care for the world and people, try to make the world a better place, and take ownership of your choices but don't let guilt and anxiety dictate your choices.