I never really wanted kids. My niblings have benefited from me caring for their grandparents as it freed their mum up to be with them instead of away at her parents' house. They also benefit from me being another caring adult in their lives.
I also cared for my husband during years of being ill, and I have intensely supported friends. I also visit people when they're in hospital and do not shy away from friends who develop serious illnesses like cancer or who are bereaved. (Many do disappear at these times.)
I'm childfree, but I'm not selfish, at all. I went above and beyond for my parents and did every little thing I possibly could to make their lives better when they were ill and bereaved, to the significant detriment of my own life. For years.
I know parents who absolutely do not give a flying f*ck about anyone else but their DC and maybe their DH. They're completely obsessed with their own genes. It doesn't take much to love your own children; after all, they're half you anyway, so it's like loving yourself. You're getting something out of it, not least someone to check on you and help you out, at least to some extent, in old age, even if the grown kids don't live near. There is something in it for you in the future when you have children, unlike when you care for elderly parents or do charity work.
I wonder how many people would have kids if they had a magic crystal ball and could know in advance that they'd have no help of any kind whatsoever in their old age from said kids?
I'm just a bit suspicious of some parents' halos, that's all.
Ultimately though, all these accusations about selfishness are silly. People do what they want. Those who want kids, have them (if possible). Those who don't want them, don't have them. We all live in service to our wants.
I think accusations of selfishness come from those who resent the intensive caregiving that child-rearing entails. If you enjoy raising your kids, you'd be feeling very sorry for those who don't have them, not assassinating their characters.