Nationalism is not altogether useless, and globalization is not altogether a positive force, but in terms of a guiding ideology for a country or people striving for more globalization -- fair competition across all borders, easy immigration for those from similar cultures -- is clearly virtually always better.
Why the clarifier? Such has obviously not been the result (we can debate whether or not those from different cultures easily assimilate, but it's obvious that we're drawing cultures from an extensive array of different backgrounds into physical proximity).