Earlier quoted context omitted.
So that the other side knows they're talking with (and maybe talking about, or sending resources to) a real human being who actually is a rural African kid, and not with a server farm of some sleazy US advertiser who autogenerated a fake profile.
Now, that is mixing up a whole lot of different problems, isn't it? First of all, "proving that this human being exists" in no way implies "proving that this human being is a kid in rural africa". Let alone "proving that this human being is a kid in rural africa who lacks resources". Now, those absolutely might be legitimate concerns in some scenarios--but how would that be a baseline requirement for a system for soc…
But you see those people, with your own eyes, and thus know they exist. Maybe in 50 years we'll have robots indistinguishable from humans, and the question of proof will become relevant for in-pub interactions. For now, the question is relevant only for long-distance communications.
> How is trusting one centralized, not democratically controlled institution to take care of the problem even a solution? If you rely on them, you implicitly also give them the power to effectively declare real people non-existent.
True. But so is the case with a democratic government, and so is the case with any other organization or system. And the power to declare people non-existent is exercised frequently, often by mere bureaucratic accident. Ultimately, trust is a spectrum. No organization is worth 100% trust, but also no one is worth 0% trust. I don't e.g. particularly trust Facebook, but I trust the social web - if I have a friend who has a friend who has a friend who is a friend of the rural kid in Africa, I can with high confidence assume the rural kid in Africa exists[0].
So yeah, in my previous comment I mixed up a few different use cases. But I think in pretty much all of them you want to at least know the other person is a human being, and frequently you also want to know they are who they say they are.
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[0] - This effect is actually sabotaged by the pro-privacy efforts to hide as much information about people as possible, rendering users unable to follow the social web chains beyond their own direct connections. Privacy is important, but it's always a trade-off, sometimes trading off genuinely useful things.