First off, clarification:
What exactly do you mean by "allergic"? That's pussy-footing around a term as I've ever seen before. Unless you seriously mean "Do Americans break out in hives when facing negativity?" I mean, aside from the terrible word choice ("allergic") I think every country breaks out in hives whenever someone responds to their way of life negatively. People understand that they are not perfect, but they sure as hell don't want anyone less than perfect remind them.
Tell me, are you talking about American's as the entirety of the people within the United States' or Americans as a term for the government. Those are two separate beasts.