Because the simplest ones are already in use and threatening us.

Anyway, the most dangerous weapon is the human mind (if it is determined to kill, it will; but if it can be convinced otherwise, it will be used to build a better world for itself).
I can't help but think more and more weapons circulating are inevitably turning against their builders or sellers. If one attacks, he'll be attacked back.
But it will end and depending on the way the conflict is solved, peace will last or not.
Somehow, installing a US adminstered power in Iraq reminds the world of colonies.
The locals won't like it too much and it will therefore be harder and harder for that administration to leave the area as it wil either be a catastrophe to the few local allies on the spot or a humiliation to the country that put that adminstration in place.
Let's suppose the Iraqis are pleased (peace is back, commerce is back, people smile again).
But how about their relationship with their neighbours? This is quite different from Japan after WW2: there was only one coutry at war and all the neighbours were glad it was over and peace came back because Japan alone had to face its past. Now, the neighbouring arab countries have no particular reason to hate the Iraqis (they're all Arabs) and what happens to the Arab relationship between an occupied country and an non-occupied country, both from the same culture? I don't know but it isn't promising.

Raoul