While I am not sure there is a binary opposed premise that prevents a political society from embracing both elements, I think that a reason why national security is vital to civil rights is that the latter often falls victim to the former when the former is in jeopardy. For example, when national security is at risk, civil rights is usually the first thing to be sacrificed. Consider the bombing of Pearl Harbor as a threat to national security and the internment of Japanese Americans and Japanese people in America as the response. When national security was perceived to be under siege from Communism, the resulting HUAC hearings helped to do much to undermine civil rights. When the attacks of September 11 destabilized much of American national security, the Patriot Act was passed to ensure that civil rights would be secondary to the issue of keeping the nation "safe." I think that this sequence highlights that, for better or for worse, when national security is threatened, civil rights usually ends up being on the chopping block. In this light, I think that a relationship between both is evident, suggesting one might trump the other in political reality and daily execution.