where i think the no-take-off people get hung up is that they think the plane body itself isn't going to move because of the conveyor belt. the plane body will move because the engines will push the air behind it, causing the plane body to move. the conveyor belt moving at the same speed as the plane doesn't mean anything to the plane body, just to the wheels. all it means is that the wheels will have to spin twice as fast as the speed of the plane. but they wont stop the plane from actually moving.

try thinking of it like this...say you have a hot wheels car, and you put it on a treadmill. if you hold the car, the body doesn't move, but the wheels do. if you push on the car body, you can make it go faster than the treadmill. even if the treadmill is on full speed and going 100mph, you would still be able to make the car go faster than it. it doesn't mean the car would be going 100mph, just the wheels.