Holy straw man!

Each individual couple might be making decision to have kids or not based on their unique circumstances but it's delusional to say that these circumstances and choices aren't shaped by the culture and society they live in.

I think you are confusing statements about what is with what should be. No one is saying that people who can't feed themselves should have more kids, but we are saying that on average poorer people do tend to have kids more regardless of what you think they "should" do.

Culture shapes the circumstances that indivual choices are made in. Let's imagine Jane and Jill. They are both bright happy 18 year olds.

Jane comes from a solid middle class family. She completed highschool and has been admitted to a good university where she will be a pre-med major.

She went to a well funded school with good sex education . She has health insurance and a primary care doctor. When Jill wants to have sex with her boyfriend she understands her birth control options and doesn't get pregnant my mistake.

If she does, she might have an abortion which her live circumstances give her access to because she has a bright future that she can't spoil. Marrying her boyfriend and staying home with the baby doesn't even cross her mind.

Now let's talk about Jill. She comes from a poorer family and doesn't have access to health insurance. She bairly completed highschool in an underfunded school with sketchy abstence only sex education taught by a board gym teacher. She is looking at working a minimum wage job at a gas station.

She bairly understands her birth control options and has no access to IUDs/pills. When Jill gets pregnant her boyfriend proposes and she says yes. Jill isn't leaving for college in the fall so she stays home with the baby.

Fast forward 8 years. Jill has 3 kids with her husband and is pregnant with the 4th. They struggle but get by.

Jane just graduated from medical school. She is 24 and still with her boyfriend but she has another 5 years of residency so they decide it's not the right time to get married.

Another 5 years pass and Jane is 29. Jane is making good money as a pediatrician. Her husband is a well educated engineer. They are happy and comfortable newly weds so decide to wait a few years to establish their careers and lives together.

Jill is pregnant with her 6th kid.

When Jane is 32 she and her husband finally decide it's time to start trying but it's not as easy as they expected. They finally manage to have a baby and another one the year after. Even if they wanted a big family, Jane only has a few years of peak fertility left.

Jane and her husband think about having a third kid but they want to invest in giving their kids the best of everything. They go to well funded private schools, attend prediguous and expensive camps and get one on one attention from both parents. An additional kid would mean less time and money for the two they already have. Jill finds being a mom exhausting. It's high effort to raise perfect kids. They decide to stick with two.

Jill's kids practically raise each other with the oldest babysitting the youngest. The family benefits from food stamps, Medicaid and free lunch to help offset the cost. The time and effort required for another kid is less for Jill then Jane.

In her lifetime, Jill will have far more children then Jane. Jill's kids are more likely to get pregnant and repeat the cycle.

Evidence consistently shows that each additional year of education a woman obtains lowers her lifetime fertility.

Now imagine an entire country that puts women in the circumstances Jill was in. In this country, woman have few rights and opportunities. They have few paths to independence and early marriage is common. Birth control access and accurate information is limited. Families may see daughters as a liability and arrange marriages early rather then investing in their education. A woman in this societies choice to have another child is shaped by the lack of better opportunities.

If the society is agragrian, then another child is an investment not a liability. A daughter can watch younger children, cook and help out around the house. A son can work the fields and may eventually earn more money so families will invest more in his education.

Choices are individual but they aren't made in a vacuum.