I think that nationalism is abhorrent but respect that your views are at least consistent. American isolationism would be a most welcome change from the current state of affairs.
Personally, I think that Nationalism is the only reasonable basis for citizenship in a country. If one is not truly committed, devoted, and loyal to that country, why are they there to begin with? Likewise, why would one retain any loyalty or devotion to a country that they have left? For example.... my paternal great-grandparents Adam and Karoline left Germany in 1910. The next time they had any contact with the portion of their family they left in Germany is when two of my great-grandfathers cousins showed up on their doorstep in Connecticut in 1928. Adam's belief, and that which has been handed down on that side of the family for the last century (including several of the intermarried families now) is that we are AMERICANS and AMERICANS ONLY. Where we came from means NOTHING.
I think that American Isolationism would bring about some very interesting things in the world. Including some things that foreigners may not like. The form of Total Isolationism I espouse would mean no medicines, food, money, or any other form of aid would be leaving the United States for the "developing nations". There would be no aircraft carriers treating tsunami victims. No American search teams digging through the rubble after earthquakes. It would also require some MASSIVE and MAJOR changes in American culture as well. Travel would largely be a thing of the past. Individual communities would have to start providing for themselves again. We would have to go back to a more agrarian, less technological, and hopefully more morality and values driven society.