Raptor,
If any of the objects on that list above are used, it means the country employing them has already failed to achieve victory, and is now settling with taking the winner down with them, or feels it cannot win a war, and is using a strategic strike to eliminate the enemy's forces, which is only going to precipitate a response in kind.
Nuclear, bio, and chemical 'weaponry' are not meant for the battlefield. They are instruments of statecraft, not weapons of war. A weapon's strike can be guided to a particular target, and a weapon of war is meant to be used on soldiers, not civilians. NBC devices are not, by this definition, even weapons.
They are used to demonstrate superior capability to those nations who do not have them, and to assure those nations who do that a response in kind can be expected if such are used upon the nation which possesses them. The US, the USSR, Great Britain, France, and China have not been in direct military engagements with any nation that had nuclear weapons since that nation had them. The reason is because such a nation could 'take them down with them' if they were losing the battle.
The US has a clearly decisive advantage over any other nation on earth in a conventional war, and against even a sizable coalition force. Why then has it not pressed this advantage? Because the USSR, France, GB, and China would not permit such a hegemony to be created without acting. Admittedly, GB would probably join the US, and now probably the former USSR republics, but that still leaves the Chinese and the French. All you'd end up with is another, much larger, Cold War.
Unless, of course, one side or the other attempted a pre-emptive strike, to eliminate the other side's nuclear capability. The Chinese are flat-out incapable of this. They cannot infiltrate the US in sufficient numbers to do the job by hand, and their fleet of missiles is too small to even attempt the task. Don't quote me on this, but I don't think the French have any ICBMs. I could be wrong. Even if they do, I can hardly countenance the notion that they have enough to take out the entirety of the US deterrent force. The former USSR's fleet of ICBMs is rotting in the silos, except for the ones that are being sold on the black market.
The US is easily capable of launching a surprise stealth attack on the Chinese missile fleet, and assuming the French have no missiles, the planes they'd have to strap them onto are as vulnerable to attack as any other planes. So why doesn't the US do it? Because it is a democratic republic, and if the leaders in the US ever tried anything like that, they'd have a revolution on their hands.
So these devices are going to stay where they are, in bunkers and silos. We can't put the genie back in the bottle, so leaving him there will have to do.
No nukes is good nukes.