Ultimately, the idea of the Supreme Court as a dictatorial junta is just borderline retarded for an entirely different reason. Normally, if one wants to be a dictator, one needs some sort of enforcement mechanism for said authority. Seeing as how the court lacks this, and that its decisions only carry as much weight as the enforcement efforts of the executive and legislative give them, the court ruling that the president couldn't conduct foreign policy would have roughly the same effect as me standing on a street corner shouting that I'm the king - both would be ignored.
In other words, if, McCain is elected president and he says that moslem terrorists will be kept in Guatanamo irrespective of what the Supreme Court says - then we can't expect you to whine that McCain is tearing down the Constitution and committing the coup? Correct? Cause it would be completely in line with what you said here.