Long flights can become incredibly boring for crew and so the 'get them all to sleep' theory doesn't always hold water. Believe it or not most (sure, not all) crew aim to please the passenger. From experience, passengers can start getting restless and irritable if cabin service takes a while and as a consequence the lights are still on and when the lights are turned down, the closing of the window shades facilitates a passengers rest.
On various forums I have found the protests of enthusiasts to be very selfish and the subject is usually only emotive when it comes to that community. This in itself suggests that the vast majority of passengers would rather do something that helps achieve a restful flight for themselves and others.
In the AF situation as mentioned by Hartington, if I was the crew member I would have asked him politely to pull his window blind down as this would give him the opportunity to enquire why he was being told to do so. If he then chose to open it again, I'd tell him to close it again.....albeit in a polite manner.
On all the long haul flights I've flown on as a passenger the window blinds have only been closed if sunlight will disturb rest. i.e if a flight leaves HKG at Midnight and arrives into LHR at 0500 in Winter then theres not really much point in closing the blinds as it's dark all the way. Perhaps this is what happened on another posters return from SIN where as the outbound flight requested the blinds were closed as sunlight would restrict rest.