History is uncomfortable. Revising it to tell lovely stories is all well and good for building a national identity.
However, sugar-coating, ignoring, or even flat-out erasing parts of history benefits no one. People started writing events down accurately because the orators of old never intended paint an accurate picture of the past. And therefore lessons learnt from the failures of humanity (lost causes, preventable catastrophies, perspectives of people on the wrong side, genocides, etc.) were also lost.
History should be uncomfortable, so we can collectively learn and have a chance to do better the next time.