Fair enough. Having a car and travelling and having more clothes than you need are technically irrational decisions as they aren’t essential, and they are detrimental to society as a whole (air pollution, climate change, resource consumption) and you will eventually suffer in the long term as a result of having dirty air, and fewer healthy young working people to pay taxes to fund the NHS. They also involve you spending money that you could be saving or using to hoard resources in the event of another pandemic, recession, extreme government or other unforeseen geopolitical / socioeconomic shock.
Not saying you shouldn’t have these things. Just saying that we all make decisions that are personally beneficially but ultimately not rational. Having kids is one such decision, going on foreign holidays is another.
The negative consequences of having kids often aren’t obvious or guaranteed or foreseeable. Who could have predicted that Brexit, a pandemic and then the Ukrainian war would have plunged the country into a cost of living crisis that will mean many families can’t afford childcare for a few years, when if none or only some of these things had happened they would have been financially okay. Who can predict a sudden redundancy, or the diagnosis of an illness or disability, or the untimely death of a partner, any of which could plunge you into financial insecurity?
If we only ever did things that we knew would DEFINITELY work out okay for them at an individual level, nobody would have kids at all - which for us as a species would be ruinous. Or buy a house, or leave the house, or get on a plane, or do anything