It shall be the duty of the Historic District Commission to exercise aesthetic judgment in connection with maintaining the desirable character of the Historic Overlay District, or designated landmarks, with reference to the style, materials, line and detail, among other things, and, insofar as possible, prevent construction, reconstruction, alteration or demolition out of harmony with existing buildings and thus to prevent degeneration of property, safeguard health, prevent fire, promote safety and preserve the beauty and character of the Historic Overlay District or such designated landmarks.