Agree that people are being a bit obtuse here. Someone who neglects or abuses a pet is surely more likely to neglect or abuse a child. And if you can’t afford food and vet care for a pet, you’ll probably struggle to provide for a child.
Yes, most children do eventually mature and gain independence, but they live much longer than your average pet, and can speak up for themselves if they think your parenting is/was substandard. It’s also much more socially acceptable to get rid of a pet if you can’t cope or just decide ownership isn’t for you. Where I live (not UK) the animal shelters are always full to pint of having to euthanise, and it’s fairly common practice to drive a dog you can’t look after/don’t want anymore into the countryside and abandon it.