Preventative wars in the nuclear age

On Sunday, the Washington Post had a front-page story reporting that the Pentagon has drafted a revised doctrine for the use of nucelar weapons by the US army, "requesting presidential approval to use them to preempt an attack by a nation or a terrorist group using weapons of mass destruction. The draft also includes the option of using nuclear arms to destroy known enemy stockpiles of nuclear, biological or chemical weapons."
Although this is described as a policy of pre-emption, it in fact allows for preventative strikes using nuclear weapons. "The first example for potential nuclear weapon use listed in the draft is against an enemy that is using "or intending to use WMD" against U.S. or allied, multinational military forces or civilian populations."
Just as the invasion of Iraq was preventative - not pre-emptive - so the doctrine invoked to justify it is being extended to the use of nuclear weapons. The distinction is important: pre-emption means that if the enemy launch nuclear weapons, and they are already travelling towards their targets in the US, the US can respond with nuclear weapons, before the enemy's weapons have hit. Prevention allows for the US to judge that an enemy is "intending to use" WMD - and this is very much open to interpretation and speculation. The US government was (it claimed) of the opinion that Iraq were intending to use WMD before the 2003 invasion was launched. Evidence that such weapons exist, it seems, is not necessary.
Well, what does all of this mean? Are the 'rules of engagement' really changing? I don't believe so. These revisions are not so much to alter the way in which the military may act, but to prepare the public for such a change. If the doctrine is asserted in advance, and accepted on a theoretical level, it's easier to sell it should it ever have to be invoked to justify actual strikes.
Should we be worried? In a sense, we should - the Bush administration, by making doctrines such as "illegal but legitimate" (not their invention, incidentally - NATO's attack on Yugoslavia in 1999 was as illegal as the invasion of Iraq) and "preventative" nuclear strikes normal, sets dangerous precedents, considering the damage nuclear weapons can do. Those interested in avoiding ultimate doom ought to oppose these doctrines vigorously, therefore.
Nevertheless, these doctrines do not in themselves make war more likely - starting a war is contingent on many other factors, the most important being domestic opinion. Iraq is a catastrophe, but those who oppose war and favour justice may be able to make significant progress in the wake of the domestic political crises it has produced (sadly, this seems least true of the UK, where terrorist attacks have put a stop to everything, including an incredible movement for global trade justice).
Surely this is a dubious doctrine for the times, but rebuilding disarmament movements and opposing militarism and war can only start in one place. We the people....