I don't think it's particularly difficult (or schizophrenic) to be proud of what we have achieved as a nation (vis a vis standard of living, long lists of Nobel prize winners and technological "firsts", etc, and the entire "democratic experiment") whilst also acknowledging that there are nontrivial parts of our history that we ought to be ashamed of ourselves regarding (slavery, racism, japanese internment, indigenous Americans, etc).

You don't, after all, have to average the two together to get a "meh" opinion of the nation. If you do that, it seems to me that you minimize BOTH the good and the bad in our history.