Random Security Measures

[Cadaverous Pallor]

If I were you, I'd email the airline and ask them why...when their only answer is "because it makes you safer" you can add your experience to the Wikipedia entry that Moonie linked to.

[DreadPirateRoberts]

I think this may be more of a safety measure, than a security measure. Taken from here:

Shades up on takeoff and landing. “Why?” a reader asked. “Sometimes I think the flight attendants are just on a power trip. Here I am, pupils scorched by the sunlight, desperate to get some shut-eye, and I have a flight attendant yelling at me to put the shade up.” Answer: In an emergency you will need to have the shades up so you can see what is happening outside the aircraft.

If something bad is going to happen on an airplane, it's probably going to happen on takeoff or landing, so it makes sense to be aware of the environment outside.