Why do people think that childfree people are immature and selfish?

Marriage isn't living outside of yourself for another person? What about taking care of extended family?

People probably think that the ones who choose not to have children don't have anything to lose and fear them. I myself never wanna have children not because I'm "selfish or "immature,' but because I couldn't be the kind of father I'd like to be, and I wouldn't want children pestering me to buy them Iphone or whatever when I can't afford them.