I’ve always thought “selfish” is the wrong word.
Of the women I know who have chosen not to have children, their reasons are always self-centered: as in, I like my life the way it is, I don’t want to have to put other people first, it looks like such hard work, I don’t want to put my body through that etc etc. So, the reasons all revolve around what she wants and doesn’t want, there are no reasons beyond her own wishes and desires.
Of the men I know who have chosen not to have children, their reasons are a mix of haven’t found the right person, can’t bear to bring a child into climate change, don’t want the responsibility, don’t want to be tied to any particular woman for the res of my life. So, a mix of self-centered and not.
(I’m passing no judgement on anything, just explaining what I see.)
So I can see why people use the word “selfish” but I don’t think it’s the best word to use. Maybe self-centered or self-absorbed? All these words are laden with connotations though, which may not necessarily be fair. So I stick with none of my business/nothing to do with me.