Adoption enables people to become parents without increasing population. Why didn't rms address this obvious objection? I think it simply didn't occur to him.

Now consider that in the context of his line: "Having no dependents, I could dedicate myself to what seemed right rather than to whatever someone with money told me to do."

Adoptive or foster parents aren't doing what seems right to them! Why are they wasting their time providing parental love to children in need, when they could be writing emacs patches?

As a child of both foster and adoptive parents, I say: What a jerk!