There's a big difference between looking in a mirror and looking at a 3D display. The difference is the same as the problem that 3D displays cause for your eyes. When you look in a mirror your eyes are focusing on the objects reflected in the mirror, NOT on the mirror. When you look at a 3D display your eyes are focused ON THE SCREEN, not on where the pseudo 3D objects would actually be. It is this difference between where our brain thinks an object is and where our eyes are actually focusing that could make 3D displays dangerous for your eyesight in large doses. It is not the same as looking at things in the real world.