Its the same argument we saw in the early 2000s and the early internet. When the anarchist cookbook and other similar materials were circulating online there was a big panic over democratized terrorism, and a push for regulation at the ISP level.
Turns out that didn't play out as everyone feared because, well, the instructions themselves aren't useful unless you also have a lab, precursor chemicals, and everything else actually needed to make a weapon. Same back then as it is today.
Any information or instructions an LLM can surface, a sufficiently motivated bad actor can and will also find themselves because the information is already online, both on the clear net and dark web.
I think the reality also is that there just isn't many people who want to do stuff like this. Like the reality is that a guy with 200 in cash could put together a shitty walmart drone with a pipe bomb attached and terrorize more or less any event he wanted. Maybe a llm that could talk you through every step involved would make it more common but it's easy enough I kinda doubt that