Except his old knife he already had with him isn't made for exploiting the flaw in the vest, so it doesn't work. He needs to go home and build a new one, and the people in the mall can go home before he comes back, now that they know their vests are flawed. Otherwise, someone who comes in and is aware of the flaw when the users are not, can stab everyone, and they'd have no clue they were vulnerable.

In real-world terms, the kind of mass-exploitation that people use to fear monger about disclosure already happens everyday, and most people don't notice. The script kid installing a monero miner on your server should not be driving the conversation, it should be the IC spook recording a journalist/ dissident/ etc.

> Just that, in the world afterwards, you must take responsibility for everyone knowing, including people who did not know before and abuse that knowledge.

This is just a generalized argument for censorship of knowledge. Yes, humans can use knowledge to do bad things. No, that does not justify hiding information. No, that does not make librarians/ researchers/ teachers responsible for the actions of those that learn from them.