I didn't argue a stronger social safety net would fix everything, just that having a weak one exacerbates the financial concerns, and is the major factor that would tip-over those who are not having children for mostly economic-reasons.
That being said, I think the critique you're getting may be more fair to your post than you think. You bring up things like college debt and high medical costs, which are not US-like in most of the places with the lowest birth rate, and the day care situation, which often isn't either, in previous paragraphs.
I do think that even if we don't note that the post was likely US-centric, we'd struggle with the fact that it's the poorer people in the US are having more babies than the richer ones when trying to apply your explanation.