How is a gun that can kill millions in a minute different from a WMD?

I had read a similar story a few years back in a magazine. What is this World coming to? How can the World stop Iran, North Korea and many others that will eventually pursue this bandwagon to stop developing nuclear weapons, when guns of this kind are being developed? At least for now the nuclear weapon states such as United States, France Pakistan, India, Israel, China etc. have promised to behave nicely, but what happens if all hell broke loose such as another world war or something starts? It just looks pretty scary and hope never happens. But World history is evident that chances of happening are more likely than not. With Iraq war and current situation with Iran, things are not looking very promising. I really don’t have any opinion against or for this kind of weapon development, but sometimes do think that a weapon like this can finish small communities like Sikhs or Jews or Bahai etc. within minutes if an aggression by a majority government or culture ever takes place. On a second though, I can’t be worrying about stupid things like this. Waheguru will take care of us all. Please read and comment if you like:
http://upi.com/SecurityTerrorism/view.php?StoryID=20060120-070112-5273r