I think this way of looking at things is rather recent historically speaking, and may in fact be part of the antinatalist sentiment you are trying to refute. Globally, improved standards of living have decreased birthrates, not increased them. If the real reason was finances, this would not happen. I think you have to consider peoples' shifting priorities, and look at what is expected culturally.

Look at our recent ancestors. There was a baby boom after WWII when times were good, but before then in the 1930s, people still had a net positive birthrate. This was true throughout our history except in the very worst of times. People simply prioritized having children. Children were the luxury. People were willing to have leaner times in order to have children. They were not considered a burden or a drain. They were a gift, for which a temporary sacrifice of small luxuries was considered worth it.

One could argue that the increased availability of contraception was a big part of the cause, and that people wanted less children but couldn't achieve that. But really contraception was available long before birthrates started declining, and what changed most of all was cultural attitudes towards contraception.