I hate to do this but this then becomes a "only bad people with a gun kill people" argument. Even most but the most ardent gun rights advocates in that scenario think they shouldn't be extended to very powerful weapons like bombs or nuclear weapons. In this situation then, this logic would be "sure this item allows a person to kill thousands or millions of people, but really the only person at fault in such a situation is the one who presses the button." This ignores the harm done and only focuses on who gets the fault, as if all discourse on law is determining who is a bad guy or a good guy in a movie script.
The general prescription (that I do agree not everyone accepts) society has come up with is we relegate control of some of these weapons to governments and outright ban others (like chemical weapons, biological weapons, and such) through treaties. If LLMs can cause so much damage and their use can be abused so widely, you have to stop focusing on questions about whether a user is culpable or not and move to consider whether their wide use is okay and shouldn't be controlled.