How's this for a sensible compromise?, I fly for an airline in the UK and it's quite simple, close the blinds where people are sleeping and there are vacant window seats, and let the fare paying window seat guests that are awake choose for themselves. Why upset your customers by being inflexible over it?
Incidentally I will challenge any cabin crew member over this if I am flying on a ticket I paid for myself, but generally I will only crack open the lower part of the blind unless it is a normal daytime flight.