When it is being deconstructed to support a particular agenda. Look at the re-writing of history today such as suggestions that curricula should be rewritten with gender neutral pronouns (obviously the author was bias, sexist or racist in "one's" use of them in the past!) and the denigration of 'truth' today as being nothing more than an association to a certain social construct. Liberal or left-leaning politics is very evident in education (I used to be a teacher) and the history class is a perfect place for the dissemination of such thought for the left.