The argument in your original post:

>So I would say we need more kids in the world if we want to have a better future.

is funny because birth rates are at the lowest they have ever been. So it is brings up the question that if insufficient kids are the problem, then how did we end up in the current world?

There's a name for this fallacy: "Reducto ad absurdum"

A minority of people not wanting to add to the population growth (and being OK with that decision) will never incite the death of humanity.

> So let's die out as humanity?

No, let's start reducing our population to somewhat sustainable levels. We can always start having more children it the future.

Yes, let's escalate slightly less than completely unsustainable exponential population growth as "extinction".

In same manner: "So let's kill other animals instead."