I agree to a point. I doubt they could manufacture a strong enough toxin and method of dispersion to cause huge numbers of casualties. It would probably be more like the Aum attack in Japan where many got sick, but the actual deaths were low, due to poor quality homemade nerve toxin and crude dispersal methods.
This, on the other hand, would be a different story. I know the chemical shells found in Iraq are after the planned attack, but that really isn't my point. People like to say there were no WMDs, but there were. After that, they say there were no stockpiles to justify the invasion. Well....a single drop of this type nerve toxin can kill. There are a lot of drops in 17 shells. People would rethink 'stockpile' if something like this were ever realeased in a NYC metro station.