Short of telling your fellow pax about your "phobia" or "anxiety", I think you did the right thing. I don't believe that you're under any obligation to lower the shade, as the FA announcements tend to be along the lines of "as a courtesy to your fellow passengers, please lower your windowshade during the movie..." You tried lowering it halfway, then almost all the way. In my book, you tried to accomodate your fellow pax more than enough, and the other pax should have been a bit more compassionate.

As far as not being able to see turbulence goes, I've always been told that observing the horizon or some fixed object is a good cure for motion sickness, so I think there's some grounds for saying that being able to see the ground alleviates your nervousness when the flight gets bumpy.

Again, I see your fellow passenger's POV, but you were in the right, too.