Spot on, it's so sad to see this kind of thinking so ingrained in people, when literally 3 seconds of critical thinking would lead to the opposite conclusion. Are kids just as selfish as adults, at every age? Does their selfishness change depending on what they're taught and how selfish their role models are? Is selfishness among adults at the exact same level across decades, eras, cultures, nations?

If the answer to any of these questions is "no" (and anyone capable of using HN should realistically be answering them as such), then it's abundantly clear you can't just hold up your hands and say "oh well, everybody is inherently selfish, 'ts just the way it is". Even the idea of everyone being somewhat selfish isn't really true when you consider the countless cases of people literally sacrificing their own lives through history - and not for some kind of post-mortem glory. One can argue semantics over that still being "selfish" as it's done to further a goal of themselves but that's just wasting everyone's time.