You are presenting a false dichotomy. The choice is not between everyone having children and no one having children.

Stallman even addresses your objection in his post:

> I don't wish that nobody had any children; I don't want humanity to disappear.

Implications would be that future generations of people would have a functional planet to live on.

Stallman is making the argument that it's acceptable to not have kids for very good reasons, and that many people might be better off not having kids. He is definitely not saaying everyone should stop having kids.

I think all too often people who will turn out to be horrible parents are pressured into having kids. Not everyone should have kids.

This is a site which works through further arguments.

http://vhemt.org/

He addressed that: "I don't wish that nobody had any children; I don't want humanity to disappear. But there is no risk of that; for the numbers I could hope to influence, the influence is for the good."

We can perfectly have a few billions less of humanity and be totally fine.