The objection to preventive war that is perhaps the most compelling is also, unsurprisingly, the most common. It is that to the extent that the prevention of future aggression is accepted as a just cause for war, the constraint against the initiation of war will be correspondingly eroded. For the claim that another state will, unless prevented, engage in aggression at some point in the future can be cynically exploited as a pretext or public rationale for virtually any unjust war of aggression. To the extent that states would avail themselves of this pretext for the resort to war, they would also become more fearful of becoming the target of an allegedly preventive war. Given the strategic advantages of striking first, each state in an adversarial relation with another would then have an increased incentive to strike first just to avoid being the victim of a first strike. Wars for which the public justification is that they are preventive thus tend to decrease security everywhere.

The reason this objection is so compelling is that it suggests that the acceptance of a doctrine of preventive war could have dreadful consequences, particularly in areas plagued by settled animosities, such as those between India and Pakistan, North and South Korea, and Israel and most or all of its neighbors. This objection, in other words, gives us reasons, as individuals, to fear any tendency to recognize preventive war as a form of just war.