Though I am not myself an FMG --and I also understand why a program would want to prioritize American grads -- I really don't understand the disdain for FMGs in general. I have not seen any difference in their capabilities and I know some of them come from extremely competitive environments. Maybe there is some racism here (against South Asians?), though I am not sure.
As for Caribbean grads, I have also not seen anything to disdain here either, at least those from Ross and St George's. They seem to be on par with everyone else as far as I can tell.
Again, I can understand why a program would want to prioritize students from US medical schools. I'm not saying otherwise. I just don't get the disdain. What strikes me as doubly odd from such elitist disdain is the fact that so many US grads come from very humble undergraduate institutions, which would make one think that such elitism would not exist in such individuals.