I don't get it either, but having children is absolutely your choice. It's totally fine to decide one way or the other.
I agree with the post that says that a lot of this forum skews towards depressive attitudes, and that probably affects the view towards having kids. If you're so depressed that you don't think life is worth living, then it's understandable that you don't want to bring another person into the world to experience the same thing. I just hope those people find happiness and self-worth in their lives.
As for the climate change thing... While I think climate change is an incredibly important topic that needs to be addressed, I don't think not having children is a good way to address it. Living consumes resources, but I don't agree with the thought process that goes "people consume resources > therefore people are a waste of resources > therefore people shouldn't exist at all." That's an insanely reductive and pessimistic view of human life.
If you think along those lines, then human extinction is the fastest way to stop climate change, and that's obviously insane. The fact that a fair number of people on this forum seem to lean towards this sort of thinking links in to the whole depression thing.
You're more than the air that you breathe and the food that you eat. Everyone is.
Depression is the only thing that can explain a lot of the stuff said around these parts.