Did everyone here skip US History in high school and college? One of the main reasons for creating the Constitution was that the Articles of Confederation made it too difficult for the government to use military force against US citizens on US soil, e.g. Shays's Rebellion. The Constitution allows Congress to raise and use an army -- such as through an Authorization for the Use of Military Force -- and to destroy "Insurrections", i.e. US citizens on US soil. And when the President swears to defend the Constitution against "all enemies, foreign and domestic", what did you think "and domestic" means?

And no, you don't have a Fifth Amendment to not be shot at when you join the enemy during a war; and no, being a citizen does not give you rights, and the Constitution does not grant you rights. The Constitution grants the government powers and limits those powers. All people inherently have rights by virtue of being born. Read Blackstone's Commentaries; the Founding Fathers did. That was the standard law textbook in the colonies at the time of the Revolution.

Remember that this whole drone nontroversy arises from the killing of al-Qaeda's leader Anwar Awlaki and a few of his followers who all happen to have been US citizens and who had invaded Yemen and carved out their own country there. The drone question is not about hypothetical harm done to innocent Americans, it's about whether the army may use military force on al-Qaeda when there is a Congressional law explicitly directing that the army do so. Why is this even a question?