Well 9/11 would have seemed a perfect fantasy on 9/10/2001.
But within matter of few hours the rate of american killed by terrorists went from same as those killed by furniture to few thousand times. The central argument is that a comparison with death by furniture is irrelevant, since the risk profiles are significantly different. Finally one cannot minimize risk of proliferation of nuclear weapons in isolation from agents such as rogue states and terrorists.
9/11 only seemed like a perfect fantasy to people who weren't paying attention. There was plenty of precedent, for the general idea of crashing airplanes into things on purpose to destroy them (kamikazes), the specific idea of hijacking a commercial airliner to crash it into a national landmark (Air France 8969, and in fiction, Tom Clancy's Debt of Honor among others), and the specific idea of killing thousands of people by destroying the World Trade Center (1993 bombing).
We can come up with ways for terrorists to kill thousands of people, and people did come up with such ways before 9/11. I see no way, short of first taking over an entire country, that terrorists can kill millions.
If you think otherwise, then describe it, don't just appeal to ignorance. The "we don't know, so we should assume the worst" argument can be used to support literally anything.
"The two students who killed 13 people at Columbine High School wanted to kill at least 500 others, attack nearby homes and then hijack a plane and crash it into New York City, investigators said."
But within matter of few hours the rate of american killed by terrorists went from same as those killed by furniture to few thousand times. The central argument is that a comparison with death by furniture is irrelevant, since the risk profiles are significantly different. Finally one cannot minimize risk of proliferation of nuclear weapons in isolation from agents such as rogue states and terrorists.