The argument is actually centering around point reference for the measurement of speed.
With a plane, the speed that is important is air speed, which has nothing to do with the treadmill. Therefore, in order to attain airspeed, the plane must move forward. So if the plane is moving forward at 100 mph (air speed), then the conveyor will be moving the opposite speed at 100 MPH. The speed the converyor belt measures against the plane itself is 200 MPH. If the plane never achieves any airspeed, then the conveyor has no reason to move.
Now, if reference of speed is the plane vs. the conveyor, then the plane will never take off as it will never achieve any air speed. While this scenario is nearly impossible in the real world, it is very possible in the world of theories.
With my car on a treadmill question, if the car speed is referenced to the stationary ground like in a drag strip, the same situation is true. The car can move forward but the speed vs. the conveyor will be double. If the speed of the car is vs. the conveyor, then the car will never move....relative to the ground.
So, everyone is right, as everyone is arguing from what they see and the reference point of the speed. But, the people saying that the plane will take off are MORE right, because the correct referrence point would be air speed, not conveyor speed.
I hope that clears it up, and thanks for not letting me sleep.
So, the shortbus only takes Canuck back to Canada.