there is no reason 3D is to be considered a fad or unnecessary.
You mean, other than the fact that 3-D has already been a passing fad that came and went, twice? That's not reason enough to be skeptical?
3D on this level where it is realistic, immersive and gives the viewer a sense of depth as if they're looking through a window into the movie world has never been done. The previous gos at 3D has been the gimmicky red/blue glasses "things sticking out through the screen" 3D. The 3D used in Avatar is on a whole other, higher, level.