What is wrong with having the user say what they want? My microwave doesn't popup open the door and grab what I am holding whenever I pass food in front of it, and that is fine.
If the gesture is intuitive and simple, it can be much more efficient than a button and reduce cognitive load by eliminating symbolic abstraction.
A great example is browsing in Safari. Scrolling, zooming, and going back/forward with gestures is far more efficient than explicitly pressing buttons to do the same actions.
