I wouldn't say it is inherently selfish nor selfless, the same as I wouldn't say having kids is inherently selfish or selfless.
There are compelling reasons for why some people might not want children. When it comes to biological children, bad genes and family illnesses that have a high risk of being passed on is a good one. I suppose it could also be argued that there are enough people pushing out biological children anyway and not enough who adopt or take in children who will otherwise live in bad situations.
But barring the whole biological vs. non-biological debate, there is also the matter of not everyone having the capability, the fortitude or even mental health stability to make good parents. If everyone made good parents there would be far fewer kids struggling in the world. Some people are better off not having kids, and struggle enough with caring for themselves.
EDIT: Oh, forgot to add, there is also the matter of being able to provide for a child. Having kids when you're in a really bad financial spot isn't the best idea either, and as such I wouldn't call it selfish to avoid bringing up a child in an already financially unstable situation.