-1 on this.
Use the existing keybinds a/d instead, left/right are too useful for scrolling sideways if the image is larger than window (common if you are not in 'scale to fit' mode).
(theoretically the arrows should already do this though, per the keyboard shortcut cheatsheet)
How about you make it left and right if the image isn't scaled to its original size? (IE, by pressing the Change size button or holding Ctrl while pressing </>.)