Because not bringing them in is defeatism. Suicide in fact.

If you want to solve the problem, children are ones who can do it, and your task is to prepare them to do it.

If you flunk from this, you are the reason the world fails.

Yeah, but maybe not human children.

If anything we need more non human children on this planet, we are attempting to fish the oceans dry, there's less than 10% of old growth forests still in North America.

Almost every ecosystem on earth is severely degraded due to human activity. If aliens came to visit they might logically assume that humans are at war with nature.

We are living in a slow moving apocalypse and we don't even recognise that fact because we think that this is normal.

There is no such thing. We are the one, the unity. There is no border, no difference between "ecosystems" and "us". The whole biosphere is a single, very complex, but undivisable system. Get rid of any tiny single part, like a single human being and it responds.

In this light, I see the notions like childfree or extinction rebellion as cancer. People doing this do not even attempt to understand the real consequences of their actions.

And why would you want to bring children into the world? Because there is no guarantee those things will happen.

What if someone decided not to have children in the 1960’s because the Cold War was going to result in nuclear annihilation? They and their non-existent children missed out on decades of peace and prosperity.