that's an argument from consequences. You're saying "the consequences of believing in one ethical standard would be messy." First, that's a flawed reason for rejecting something, because it's based not on the merits of the argument, but unpleasant implications that you foresee. Secondly, I have no idea why you'd think it would lead to continual war. Just because Humans may disagree with the Klingons' values doesn't mean they'd be willing to fight a war for it. War has an element of cost/benefit analysis. And you overlook the possibility of peaceful persuasion. The Federation might be able to get many cultures to go along with it without firing a shot.