We exceeded "enough humans in the world" forty years ago. Now we're basically manufacturing food out of fertilizer, which only works until the fossil fuel runs low (or a crash program of nuclear energy, which we haven't started). The Green Revolution was an impressive achievement, but one we are not prepared to repeat.

Maybe I would feel worse about having contributed to overpopulation if other people wouldn't multiply in such an unchecked fashion.

What is the world all about anyway?

Since I have a child, I actually want my friends to have children too, so that my child can have friends, too. Rather selfishly (you might even say racist), I want my culture to survive.

The probability seems quite high that my child will be confronted with a difficult future. That held me off from having children for a long time, but ultimately, they deserve their chance. I don't need 10 children, but one or two should be OK.

That's a pretty strange and common "us vs them" mentality. Unfortunately it doesn't really work - both your children and everybody else's children are all still human, as much as some people like to believe otherwise. It also doesn't work in the same way that making your adverts on a page bigger than your competitor's adverts doesn't work: eventually both you and your competitor have adverts so big that there is no content left on the page. Then the page is just junk mail and gets tossed in the trash...

That's why I said one or two children are enough for me, not 8 or more.

Yes, it's selfish. So is living at all. If you are so concerned, why not commit suicide and donate the resources you would have consumed in the rest of your life to other people and their children?