re: How can you cognitively dissociate the our less glamous deeds from our ideals?

The winners of wars get to write the history and the narrative of what the ideals of a symbol stand for. In the end, the "idea" of our Republic are noble and good. The flag is one of the symbols of that vague notion of noble and good ideals of man, and that is good enough for me. We aren't there, but the ideals represented by the symbol is something to never stop striving for.