In the 1950s, it was novel and driven by audiences, who really wanted to see something in 3D. In 2010 it's mostly being pushed by the theaters, who are desperate to have something they can offer people that they can't get by watching Blu-Rays on 50-inch TVs at home, aside from the experience of eating half a ton of popcorn and listening to some jerk on his phone.
Considering that 2D movies have almost all the 3D cues needed for our brains to interpret them as 3D, I'm not convinced '3D' movies actually make that much sense. It's certainly not comparable to 'flying' vs 'not flying' anyway IMHO.
Oh, I haven't seen any movie that makes 3D worthwhile. It's just that the argument "people tried it before and failed" is not even a little convincing.
