The same law prevents you and me and a hundred thousand lone wolf wannabes from building and using a kill-bot.

The question is, at what point does some AI become competent enough to engineer one? And that's just one example, it's an illustration of the category and not the specific sole risk.

If the model makers don't know that in advance, the argument given for delaying GPT-2 applies: you can't take back publication, better to have a standard of excess caution.