The obvious, and most tangible cost of the implementation of the Bush Doctrine was that it led to a long, costly, and bloody conflict that cost the lives of thousands of Iraqis and American soldiers. The long-term costs of the policy remain to be seen, but opponents of preemptive military action have argued that it undermines one of the core principles of the United Nations, which is that nations should not attack others except in clear cases of self-defense. As one critic has pointed out, it "validates striking first,"
on the basis of shadowy intentions, alleged potential links to terrorist groups, supposed plans and projects to acquire weapons of mass destruction, and anticipations of possible future dangers. It is a doctrine without limits, without accountability to the UN or international law, without any dependence on a collective judgment of responsible governments and, what is worse, without any convincing demonstration of practical necessity.
It sets a precedent, in other words, for force as the guiding principle of foreign policy. As it turned out, the Bush Doctrine also entailed unilateral action, undermining the principle of coalition-building that had been established by George H.W. Bush in the first Gulf War. Preemptive action, unless justified by clear and unambiguous evidence of a danger, also can undermine American claims to morality in a conflict against terror that remains in many ways a battle for "hearts and minds." Problems with obtaining such evidence were made clear by the lack of weapons of mass destruction, which had been the justification for launching a preemptive war, in Iraq.