It was not just the fact that Lord Elgin stole the marbles as the Greeks maintain, but the manner of which he removed them, prying them loose and dropping them to the floor, that caused extensive damage to the structure of the building as well as destroying many of the pieces. It would be like you taking apart a BMW sports car with a crow bar and then trying to put it back together. New evidence supposedly proves that the firmin (decree) from the Sultan did not give Elgin permission to take the marbles. Probably you will be hearing more about this as the battle to have them brought back to Greece heats up.