Ethereum co-founder Vitalik Buterin is arguing that the digital identification approach being promoted by Sam Altman’s World project has real privacy risks.

Previously known as Worldcoin, World was created under Altman and Alex Blania’s Tools for Humanity. The organization says it can help distinguish between AI agents and human beings by scanning users’ eyeballs and creating a unique identity for them on the blockchain.

In a lengthy post, Buterin noted that World’s approach of using zero-knowledge proofs to verify human identity while protecting anonymity is also being explored by various digital passport and digital ID projects. And he acknowledged that “on the surface,” using a “ZK-wrapped digital ID” could contribute to “protecting our social media, voting, and all kinds of internet services against manipulation from sybils and bots, all without compromising on privacy.”

However, Buterin suggested that this approach still boils down to a “one-per-person” ID system, which creates significant risks.

“In the real world, pseudonymity generally requires having multiple accounts … so under one-per-person ID, even if ZK-wrapped, we risk coming closer to a world where all of your activity must de-facto be under a single public identity,” he wrote. “In a world of growing risk (eg. drones), taking away the option for people to protect themselves through pseudonymity has significant downsides.”

As a concrete example of the risks, Buterin noted that the U.S. government recently started requiring student and scholar visa applicants to set their social media accounts to public, so that it could screen those accounts for “hostility.” Similarly, he suggested that even if there’s no public link between different accounts created under a single digital ID, “a government could force someone to reveal their secret, so that they can see their entire activity.”

Instead, Buterin is advocating for an approach emphasizing “pluralistic identity,” in which “there is no single dominant issuing authority, whether that’s a person, or an institution, or a platform.” Pluralistic systems can either be “explicit” (they ask users to verify their identity based on testimonials from already-verified users) or “implicit” (relying on a variety of different identity systems) — in his view, these represent “the best realistic solution.”