You're dead wrong. You're dismissing a field of physics that you haven't bothered to study. With a spacetime propulsion field a craft can zigzag across the sky at thousands of miles per hour, and an occupant inside the craft would feel nothing because all of the matter within the gradient is accelerated uniformly, unlike all of our primitive propulsion methods such as planes and rockets etc. where the force is transferred mechanically from the thruster through the airframe to the passenger. To a UFO occupant looking out the window while performing rapid zigzag maneuvers, the view out the window would look like a movie projection being swung from side to side. No g-forces, no sense of motion at all - a very comfortable ride indeed.