I personally feel it's common courtesy to keep the shade open on takeoff and landing. I personally can't get my bearings straight on taxi / takeoff when all the shades around me are down. I choose a window when I can but obviously that's not always an option. Just happened to me actually this past Wednesday as I was sitting aisle in Exit row on a 12:20pm departure. Literally not a single shade open within 2 rows of me (ahead and behind). People did choose to turn their overhead light on though!