The wikipedia article for sarin gas is also extremely frightening, but the example Bret gives of the Tokyo subway attack shows that it’s probably less effective than advertised in a modern military context. The bar isn’t “is this stuff deadly”, it’s is it deadly enough to overcome the expense, complication, and incompatibility with highly mobile modern doctrine to make it worth using on a militarily relevant scale over conventional options.

I’m certainly no expert, so I’m not going to go any further with “is this poison poisonous enough”, but that wikipedia article at least doesn’t seem to make the case.