Should the U.S. foreign policy pursue realpolitik?In other words, is it acceptable for the U.S to do anything even something illegal or immoral as...

Individuals tend to be more moral than societies and
governments, as philosopher Reinhold Niebuhr has argued.  That is to say, one can't
expect that the government of the United States, or the leadership of any empire or
nation for that matter, would act in a way that is consistent with what most people
would call moral.

Nations act in their own self-interests. 
While sometimes using realpolitik, acting in the national interest above morality, is
also a moral action, this is usually more coincidence than anything else.  To act in a
way that put morality above economic and security is called altruism, and nations that
have come close to practicing it have often not survived
long.

It is an interesting question/topic, and I do believe
it would be easier for the US to act in a more or less moral manner with regards to the
peoples of the world if we were no longer an empire, or no longer dependent on energy
from foreign sources.