I resent someone telling me to block out the sun when it's not shining on anyone and won't for the remainder of the flight in broad daylight just so the CC can condition the passengers to sleep and be less demanding.
I generally do as I am TOLD then it goes straight back up. IF it was shining into someone's face then I would lower it, but the option is never presented.
If it's a massive problem and you feel the need to nap in what is MY daytime, then buy a little mask for your eyes.