The burden of proof has to be on the person who wants to go to war--the 'dove' should have to prove less than the 'hawk' since the hawk proposes (a) killing people--ordinarily quite wrong; (b) risking the lives of his fellow citizens (c) spending significant amounts of public money. All doves really have to do is show there isn't a sufficient reason--and in a sane world this shouldn't be hard in many cases since there should be a very high bar to justify war. Hawks have the proving to do.