Any American who is in favor of isolationism hasn't learned a thing from history - isolationism has never worked in the past ... and ... it will NEVER work in the future.
We live in a global community and the ONLY thing isolationism can accomplish, is to cut us off from the world at a time when world affairs are at their most relevent to our well being and understanding between nations is at it's most important.
With the advent of world terrorism and nationalism, neither the United States (nor an other country), can afford the disconnect that isolationism causes in our dealings with other nations. Whether it is dealing with global terrorism, oil prices, availibility of other resources or the policing of our borders ... political policies between diverse nations is the grease that lubes the wheels of nationalism and economics. No longer can nations pretend that the world is their personal bread box that can be plundered at will - interaction and cooperation between nations is a must
IF constant warfare is to be prevented.
-and-
Unless (or until), the nations of the world unite in their fight against terrorism because of religious bigotry or national hatreds, the imposition of isolationism would be the same thing as putting a loaded gun to your head and pulling the trigger.