Relatively minor military operation [ it's only minor in his head because of the number of people he's heard were involved, and look he's used to things on a larger scale ] doesn't seem as large as the possibility of a nuclear strike, to me. On a civilian population center, no less . . .

Unless they just don't give a damn. [ Which might be the step Wash is missing here, it's just difficult for him to grasp. But of course, since they ultimately did go through with it. ]