40 million commercial flights per year (ish), opening shades on 40 million flights for the 15 times that it might be an issue seems perfect for today's panicky public. (the other reason I could think of would be to open windows to make plane more visible to others taxiing on the ground...if that is the reason for this then please ignore first comment)
and what kinds of cords are you people bringing on planes...I would agree that if you are plugging in 12 gauge drop cords that it might impede emergency exit, but plugging in a typical phone charger cord wouldn't even be an obstacle.
You would be much more likely to get impeded by a strap from a bag placed under the seat in front.