Many (not all) conservatives see themselves as defenders of a particular, rather specific way of life, moral code, worldview…which they group under the heading of “values”. They think of these ideals as defining what America is about. Having staked out this ideological territory, they see it as being constantly under attack by various subversive forces, international and domestic. Some of that is real, of course, but much of it is just the world changing as the world is wont to do. But because their idea of America is so defined and rigid, all of this shifting and evolution looks to them like a threat to the very essence of America.
Liberals tend to have a much fuzzier idea about what America stands for because they think that America was constructed so as to accommodate a huge variety of ways of life, worldviews, etc. They think that America should be as loosely defined as possible so as to allow for change and evolution, because these are both inevitable and potentially healthy. There is a certain element of secular faith in liberalism that America is robust enough to embrace new ways of doing things and unconventional points of view without losing its fundamental identity. Change appears less threatening from the liberal point of view.