I have to bite.
I am one of 4, both parents self employed and working from home a lot, totally dedicated to having a happy, large family. Yet my two older siblings have always felt they really missed out as us two younger siblings arrived as they were preteens. Definitely not enough individual attention at a sensitive time.
My own two DC love nothing more than '1:1 time', despite getting on really well and already having quite a bit of scheduled time alone with either parent every week. Even if we don't do anything special, just talk, run a couple of errands, nip up to the park or similar, it's a couple of hours alone together, valuing our relationship.
You seem quite hardened to the environmental impact of having children, so I think I may be typing in vain, but here goes. The environmental footprint of a child growing up in the UK, irrespective of its parents' lifestyle choices is considerable. Adopting a low carbon lifestyle does not go anywhere near far enough toward 'off-setting' the creation of a child in a western economy. We are facing global climate breakdown. Actually facing it, as in 'it is already happening' just not to us, yet, but to other people's children, in other parts of the world. Not your fault personally, but we all have choices to make.
My greatest fear with regard to the collapsing climate, however, from the point of view of a parent, are the likely symptoms of this impending crisis, which no amount of love or good will is going to be able to insulate us from; even analysts at the relatively conservative and moderate PricewaterhouseCoopers, with no other skin in the race than to optimise client investment, are forecasting global (yes, that means here too) food scarcity and an unprecedented strain on resources in the not too distant future. This is the stuff that ferments economic failure and societal collapse. And I am absolutely certain that no parent wants this for their children.