mono-stereo This is the way numbers work Hugo. “Too many” can be any old number.
That comment adds nothing and does not answer the clear question.
Given the context, “too many” will just be any number of 1 or greater.
If the number was 1, then any additional 1 would be “1 too many”
If the number was 2, then any additional 2 would be “2 too many”
etc. etc.
Regardless of whether it is 1, 2, 3, 70 etc. etc. which you think is “too many”, then none of those will be consistent with someone both being fine with and welcoming additional births on the one hand, yet somehow saving the planet by not having a child on the other hand:
If the “too many” number is 1 then you must admonish that 1 birth as excessive.
If the “too many” number is greater than 1, then your choosing to not have even 1 kid does not mean you are saving the planet as there is still excess capacity.