I see it as an excuse and ego.
We have created this great being and formed its views to feed our egos. If we enslave an entire race, oppress the fair sex or invade a country, then we are the bad guys. However, many ages ago, mankind created this all-knowing, all-seeing being that we say has created everything. While the ancient texts of this creature make absolutely no mention of the U.S.A., we automatically assume that this creature created all of this - the universe, the planet and all - for us. It is akin to the basic egotism which lead our ancients to believe the Earth was the center of the universe. If we make ourselves believe that we are doing the work of this figment of our imagination, then we literally can do no wrong.
Of course, in history, there have been many others who have thought the same and have failed. The British empire, the Nazis, the Roman empire - each had their own gods and versions of gods, each of whose opinions they sculpted to fit their own beliefs. A couple of those were quite a bit more oppressive than others - and used their beliefs to reason that it was OK.
Fortunately, the U.S. is nowhere near as aggressive in enforcing our beliefs - however, there are some on the fringe (some who do wield some power) who have aggressively altered the views of their gods, sculpting its views to meet their own in that the U.S. is under a constant threat of its religious freedom and that the only way to alleviate this is to force the rest of the world to submit to our views.