I'm as strong a supporter of American athletes as anyone, and I'm certainly not writing to rush to the defense of Nike, but the hyper-nationalists need to dial it back a notch, and stop and think for a minute.
First of all, not to be trite or simplistic, but this is a free country. (That's what makes it the greatest, right?) If a privately sponsored track club or training group wants to add a foreign athlete, that's their right. As someone said, it's not the USOC Training Center. There are no taxpayer funds involved.
Second, the track community and these boards are full of people constantly lamenting and/or complaining about how American athletes are not up to the competitive level of their European or African counterparts. We all devour magazine and online articles about an athlete's or coach's trip to Kenya to find out "how they do it." What's so wrong with introducing a little foreign talent, work ethic, and willingness to sacrifice into some American training groups? (Particularly when it's in the form of such class acts as Mo Farah and Sally Kipyego.) That might just be one of the best ways to raise the competitive level of our American runners.
Stop, take a deep breath, and at least be willing to consider looking at the forest instead of just the next tree.