Shouldn’t the enemy at least wonder if we would?
I understand what you're saying, but no. Besides the humanitarian and ethical challenges that BIO/CHEM weapons inherently have, they are also volatile, unpredictable and in some cases unctrontrolable.
If, as I believe, terrorist are experimenting with these horrible weapons, they are certain to have some type of mishap (we had plenty of them through the first half of last century). When this happens, unless the US position is clear and public and unwavering, it would be too easy to blame us. Our position on BIO/CHEM agents must be unambiguous - always.
There is plenty of confusion in this war, but one thing the enemy understands perfectly; the US possesses the most lethal fighting machine the world has ever seen. We don't need biological or chemical weapons to kick their a$$. That's why they live in caves.