The majority of British people (not unique to them, all do it) only ever want to believe a mythologised version of their history, with all the morally questionable bits erased.

The nation myth has gatekeepers, its universal. However if you had a global empire it sure helps to understand how you impinged on subject countries if you want 'global Britain'. It creates a bond but that needs to become a positive one based on mutual respect. Ignorance is dangerous.