The decision on the shades belongs to the cabin crew. If they don't care then it belongs to the person in the window seat. The decision on whether the person in the window seat can conveniently access the aisle belongs to the passengers in the middle and the aisle seats. Window seat occupants who don't care if the glare of the sunlight disturbs their adjacent seatmates and become pissy if asked to lower the shade might want to keep that in mind or plan to cutback on their fluid intake.