Unfortunately, sometimes the only way to keep other countries from abusing their power is to keep ours and be stronger. If we keep our weapons, we can at least maintain more power in a language that they understand. They may not agree with our principles, but if they know that we still have stronger weapons than they do, they might pause before using theirs.
Not in the near future, much as I would like it to be so. The membership in the Nuclear Club is still expanding, and while I would like to see America's arsenal reduced to under 1000 weapons, eliminating would not serve our near term security interests, or the world's for that matter.
However, I see no reason whatsoever for maintaining biological or chemical weapons. If nuclear weapons are not enough of a deterrent for another nation, then nothing else will, and these are merely dangerous and expensive to maintain.
If you look at this from the perspective of realism (in the International Relations branch of political science), the answer is that there is no way that the US should eliminate its stock of WMD (at least not of nuclear weapons). The reason for this is that other countries continue to have them and still other countries continue to seek them. If the US had no WMD, there would be no way for the US to deter other countries from using WMD to attack us or other countries.
Realism holds that a country must act in ways that will keep it safe. It cannot rely on other countries to just "be nice" -- it has to assume that they might someday attack if they have the feel it is useful. By this theory, the US needs its WMDs. If we had none, any country with WMDs could either attack us or threaten us and we would have no way to respond.