Well it's definitely a compromise situation. Those of you who feel you must have your shades open for your personal comfort should also realize that you might be making it difficult for 5 or 10 other people to sleep. I could sleep if the plane had a glass dome roof, but some people have more difficulty. Sure, you're the one sitting next to the window, but is your comfort so much more important than the comfort of others? Have you ever had insomnia? It's really awful, especially on an airplane. At home, if you can't sleep you can get up, walk around, make a sandwich and tire yourself out. In the air, you're pretty limited on how much of that you can do, especially since most of your activity is still going to be centered around that same seat.
So, compromise. If you're going to open the window shade, try to work out a situation that bothers the least number of passengers, while getting you the light that you need. This probably doesn't involve having two out of three shades open.
As for the FAs, I'm quite certain that they want the shades closed so that other passengers can sleep, and to prevent them from getting complaints from passengers. I find it pretty unlikely that the FAs just want the shades down because that's the way they like it.
And finally, about passengers complaining- In my experience as an American, it's pretty rare for people to complain to others when someone does something they don't like. You may have your shades open, and maybe no one has complained to you. Does that mean you're not bothering anyone? Not necessarily, there may be people who are bothered, but do not want to get out of their seats, walk over to you and confront you. Especially if they're trying to sleep. People usually try to avoid confrontation.