Is it selfish to decide to stay childless?

I feel like if I don't post this, I think I can't sleep lol. There is this YouTuber who I like watching who is a really smart guy and really open-minded who keeps saying, "Deciding to stay childless is selfish; there's nothing wrong with that, but it's selfish." I can't understand why it's selfish. I think it's actually the opposite; why give birth to someone when you can instead adopt a child that already exists and needs a home? You give birth because you care more about passing your genes; there is nothing wrong with that, but it's not something you are doing for the sake of the world. Like, why should I think of myself having the ability to have children as a privilege? To be frank, I wish I were infertile; my life would be easier hearing "Poor woman, no one wants to marry her because she can't give birth to children," than "Look at this crazy woman who doesn't want to marry and have children."