This is just wrong.
It was commissioned by Congress. "Management of the memorial was turned over to the National Park Service, under its National Mall and Memorial Parks group. As with all National Park Service historic areas, the memorial was administratively listed on the National Register of Historic Places on the day of its dedication." (wikipedia)
I think, as the piece being commissioned by congress and the managing body by the US Park Service, the artist can go fuck himself. As an artist my self, Im possessive of my own works, but this is wrong. As a photographer, I am allowed to take someone else's work and duplicate the scene and photograph it. This is so long as I am not taking the image of their creation and claiming it to be my own. If I put the effort into it to duplicate it, and take the exact same photo, and can prove I did all that, Im in the clear. Taking a picture of a publicly commissioned art piece is my own work. Also, If I had art that was to be commissioned by congress, I wouldnt throw a hissy fit over what the government wanted to do. Theyre not even making money off it. What the hell is this guy's problem. He is known as the creator, that should be plenty enough.