Why leave the latest version of global nationalism? Let's see...

10. It costs way too much money
9. Communist China gets the same vote we do
8. We don't do anything they say unless we want to anyway.
7. Sometimes, we have to listen to France.
6. They hate our Consitution (Particularly the Second Amendment)
5. They wish to institute laws that we are to follow without regard or consultation to our Constitution, which is considered secondary to UN regulation.
4. Almost every country in it hates us, but has no problem utilizing our money and our military.
3. Remember George Washington's warning about "entangling alliances"?
2. We can form any alliance we want to without them.
1. Did I mention it costs too much?