I don't understand. How is 1 biological kid worse than 0 biological kids? It sounds like decafninja is likely planning on having 0 biological kids.
As for what decafninja (or any individual for that matter) decides upon in the bedroom, that's for him to decide and his business alone. I'm not going to comment because it's none of my business.
I'm just pointing out that in a wider discussion of "oh noes population decline oh noes low birth rates", it's not constructive to be talking about having 1 kid when there's a hard minimum of having 2 kids and ideally more.
If people voluntarily self limit the size of the population that is a good thing because it means we won't need to shoot each other if it turns out we are straining the earth too much.