I don't want to have kids not because they left a bad taste in my mouth (I still love them: they were young, made a mistake, but still tried), but because I never got to experience all the things I wanted to as a child. So my life as a 20/30 something is dedicated to experiencing the world. Finding joy in others, in travels, in food, and in contribution.
That said, if children were ever to be an option, it must be adoption. It is so incredibly selfish to say that the (non-existent) child you might produce with a partner is more deserving of safety, freedom, and a fulfilling life, than an already living person. Granted, adoption is full of its own political and socioeconomic issues.
Regardless, I have a serious driving interest in making that future better. I have no idea if it's as much motivation as a parent has, but it's still a very big motivator.
I think the "us against them" mentality is where the child-free peeps are seen as narcissistic individuals who don't take on this important responsibility. Her argument was that it's kinda of a false dichotomy, and there are plenty of ways for child-free couples to contribute to society while parents by definition, have to have priorities of their children taking place over society at large.
Not to mention it is facetious to say that parents are selfless in the first place as there are many selfish reasons to have children.
However, I'd love to hear more about people who decided not to have children and whether they felt like they have contributed to society in some other way, whether by their works, their association with their associates or associates' childrens.