Flag Day Nationalism

Here we are once again forced to look on every variety of American flag flying from every sort of venue. What an ignorant display of Hitleresque nationalism!  What makes a particular day a time for celebration? is it only that the state decree's a particular moment in time to be a special day worthy of celebration?  or is it a way to more tightly bind the people to those who claim the right to rule them? Where did the idea of collective celebration come from?