@hifiive if you’re genuinely baffled then it’s a fair question I think. Some of the questions asked regarding the potential negative impact on the planet had, I think quite a lot of judgement baked into the question, which is why myself and others wrote some snarkyish posts countering these. Mostly to show OP that there are plenty of people on here who aren’t judging her for this.
To answer your question though, the reason I can’t say that having a child is bad for the environment is the evidence isn’t all that clear that it’s “overpopulation” that is causing climate change. The top polluters on the planet are about 100 companies who are making, and politically permitted to make, profitable decisions which come at the massive cost of the planet. The bitter-sweet truth is we, at this moment, according many energy experts (e.g. Saul Griffith and his like) have all the technologies, and the blueprints for policies which we need to turn around climate change now. Or we have everything we need to get about 90% of the way there. We need to start now though.
The reality is the energy conservation model of stopping climate destruction would have probably been effective if we went for it back in the 80s and 90s. Unfortunately, conserving energy and relying on individuals to massively reduce their carbon footprint won’t make enough of a difference at this point we need to make massive radical changes at the policy and infrastructure and of course societal level. This is true even if a country like the UK legally mandated the sorts of massive individual lifestyle changes some people on this thread have laudably chosen (veganism, no children, no foreign travel low/no import foods, turning off lights, keeping the heating turned down etc). So, will another person on the planet cause another big carbon footprint? Possibly, if everything stays at it is now at the macro level. Will people opting to not having children for this reason have a significant impact on turning around climate change? No, highly unlikely. I appreciate it a good gesture and it’s better to live according to your ethics then to not do that, but I react against it because I think that even though it involves a lot of personal sacrifice it’s fundamentally an intellectually lazy form of activism if that’s all people do.
More useful forms of activism of just contributing to helping climate change significantly would be to build a career with that as one of the goals. To advocate for green policy in your organisation, To lobby/petition local and national politicians to for example remove planning policies which stand in the way of mass movement to green energy building. To petition politicians to support green investment and infrastructure, to get involved directly in politics yourself to help make these things happen. There are individual things we can do, but intimately this is about changing policy, and making good climate policy politically feasible by being educated enough to know what good climate policy looks like.
The solution in different countries will be many and varied depending on their level of development and resources but a policy of “no children” or “fewer children” is unlikely to be the answer. It’s also naturally happening in most developed countries, so even if it was a great idea (I’m not convinced it is) it would likely be unnecessary highly complex legislation which would waste time when we could be focused on policy which would be truly useful in the effort to reverse climate destruction.
Individual blaming of people who don’t conserve or recycle or use up too many resources is a distraction and it’s one that stops people from exploring what can actually usefully be done in the short time we have left to turn this around. We don’t have enough time to wait for everyone to voluntarily make these dramatic lifestyle changes.
Sorry that was a very long post- but it does sum up my answer to your question