If I understand this correctly, the first question is what limits the extent of weapons ownership by private citizens. That is to say, can a private citizen own a stockpile of advanced weapons or is there a limit weapons ownership based on potential impact of the weapons use? To this question, I would ask you to consider the question: what organization would supply an advanced weapon to a private citizen or to a military that does not respect rational principles? Only a criminal organization.

Second, if the organization is a criminal one, as you have also described, then criminal action must be legally circumvented.

Third, if a private citizen is witness to criminal activity, it is in his self interest to report it to law enforcement authorities who can best manage the threat.

john, maybe it's just the way you phrased your question that confused me. But if I'm reading you right, someone's intending to launch a WMD attack, and somehow word of that has gotten out--you're asking what an Objectivist or free society could or would do to find or stop it without a NSA type of mass surveillance.

Without going into the extreme unlikelihood of such a thing happening in an Objectivist or free society and why it would be so unlikely, let's just look at the NSA part of the question. There has been absolutely no evidence in the last 14 years that the NSA has stopped any such event or preparation for it. Just the opposite in fact, with the recent release of the drone assassination results.

The second part of your question has to do with the action following the gaining of information about someone (a neighbor) that's perceived to be a threat. If it's just an unsubstantiated suspicion or fear, it's not something that needs to be talked about. Maybe you do a little more observation or even talking to the neighbor yourself to decide if there's reasonable probable cause to believe that a threat really exists. If you can substantiate it to the point you could justify the government intruding into your activities and privacy, then report it--if not, then it's probably none of your business.

Here's a quote:
"During World War II the entire nation had been mobilized, all the talk of loose lips sinking ships, the scrap drives, the guards on railroad bridges in Iowa. Much of it was absurd when the threat was finally understood, long after the war was over. There were no legions of spies and saboteurs in America, and the few who were in place or attempted to infiltrate were caught within days by the FBI. There was a threat, and though remote, it was at least acted on back then."

Again, who sells weapons to anti-rational people? Would you sell your piece to a known criminal? Then how is it that a large weapons manufacturer would do so?