First, the case you're talking about happened during the current Iraq conflict, not the liberation of Iraq.
Second, there have been two cases during this war of hand grenades tossed into tents - one was the case involving a muslim soldier, as you described; the other involved just a regular old christian soldier.
Third, "fragging" has been a part of war since war has existed. As the 2 cases in the current war demonstrate, it is in no way restricted to Muslim soldiers, and there's no evidence that Muslim soldiers are any more likely to do it than non-Muslims.
Finally, again - getting into West Point is hard. Very hard. The type of people who are offered admission into West Point are NOT the type of people we need to worry about. They're the best our country has to offer, regardless of their religion.