Groups and individuals (and there are several) who have recently proposed banning Muslims from serving in the US military as a result of the Fort Hood massacre are demonstrating naivete and an incorrect understanding of both the military and the US Constitution.

No American citizen should be prohibited from any government role, including military service, purely because of his religious beliefs.

Besides being ludicrous on its face, the enforcement of such a religious ban would be logistically impossible.  In addition, it would negatively impact all faiths, not just Islam.  In fact, a logical outcome of such a course of action would potentially be the outright banning of religion itself from the military.

The right to believe as one wishes is a human liberty protected by the Constitution.  While there are times when the US government may legitimately restrict actions, even if they are based on religious belief (and the military has an even greater leeway to do so), American citizens should be loathe to call upon their government to treat citizens differently simply because of what they believe.