The point of using the real world as a setting is to use what the players already know as a point to grip them, and so you can assume certain basic points without having to spend a lot of time explicating them. But then, your fluff needs to be plausible in the context of the real world - otherwise, you're not just failing to make use of your assumptions, but actively working against them.
It then follows that FFG felt that the fluff text was plausible, that casting the USA as the villain of the piece (with "brutal displays", "lashing out mercilessly" and taking part in destruction of whole nations that sounds suspiciously like genocide) was believable.
That this would be a tender spot in many people's minds should come as a surprise to nobody.