One is that it lends itself to narrow minded parochialism. While understanding oneself and others can certainly support more constructive relations with the world, it naively assumes those relations are based on knowledge. The opposite is equally true. We might be more cosmopolitan or tolerant, or we might just as well become arrogant or more sensitive to our differences with others. Familiarity with other cultures or peoples might support our entering into positive relations with them, but that same familiarity could just as well breed contempt.
Most violence is domestic.
Because historical relevance in this variety of history is inversely proportional to time, it ends being profoundly a-historical. One way is to represent the past in terms that are really germaine today. Perhaps it is inevitable that historians see the past through modern glasses, but to represent it as simply a prelude to the present looses much that distinguished the past from the present. In practice, world history textbooks give far more weight to the western tradition than to others, to modern history than pre-modern. That kind of arrogance is hardly an attitude upon which to build positive relations with non-westerners.