Because the other children don't join in the rock throwing ? ;-)
As far as I know the US is one of the very few nations who hasn't signed the treaty to ban biological weapons, so there is the propability they still want to use them sometime.
And everything seemed to be fine with the US as long Sadam shot his US-delivered WMD at Iran, an "US approved targetTM" in the 80's. (because they rebelled agains the US-puppet Shah) Saddam wouldn't be so powerfull now if he hadn't had that serios backing by the US (And he USSR, and the deliveries from a lot of other nations) back then.
So we have a history of the US going in to do something, and it all turning out worse in the end.
Don't get me wrong, the US has done a lot of good in the world. But that region just seems to be bad luck for something like that.
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