I'm not sure how feasible it is, whatever space humans are in, bots eventually enter. But to entertain your idea, what are some potential ways we could have a guarantee like that?
Eve is vouching for Mal. And when Mal1, Mal2, Mal3 etc are all vouched for by Eve, then they are all trivially linked.
The far bigger problem is "how do you vouch for a single entitiy". How do you prevent Eve having multiple unlinked accounts.
So how would the interface/UX work with that, for each outgoing request you'd need to scan your retina, so you'd have something like a Yubikey at home, but with a little retina-camera instead?
Spam bots would use stolen/purchased credentials and get shut down. State-level bots would be free.
You: "Cool, we'll get tons of infrastructure in your country and make lots of money because you'll force everyone on it.
Me: "Hey, this is working out great. Bring your team over to Auth'istan for a business trip it will be great.
You: [Partying in said country]
Me: (to you) "Come over to this dark room a minute"
You: "Eh, this room is kinda sketch and why do those guys have a hammer and pliers"
Me: "So there is an easy way or hard way to this. Easy way, you give us unfettered access for our bots to spread propaganda on your premium internet. Hard way, we toss you off this building then we'll throw the rest of your team in a dark prison cell for doing the cocaine on the buffet table. Eventually one of them will give in and give us access."
Me: "So which is it going to be"
The $5 wrench is typically the winner.
The only thing you could do is build an identity from scratch, karma as you will, but then if it was actually valuable people would sell that (see rich people buying high-powered gaming accounts for the lolz etc)
I think this would limit the supply of IDs, so a big improvement over the current situation where bot posters can just farm fake IDs. Obviously this has some assumptions - for example that most humans joining the platform do so in good faith and not to just sell their IDs to bots.