Two good reasons to have windows is from a safety point duriing an evacuation in daylight hours, in the even of no electrical power, as I think was the case in the A320 landing in the Hudson river, it is alot easier to evacuate and for the crew to check the aircraft, Secondly, it is easier for fire and rescue crew to locate fire and people, that is why the blinds are in the up poistion for take off and landing.