Personally I do not think it is a stupid idea at all. Purchase any in-dash unit with video (Pioneer, Alpine, Kenwood ect ect), and they have all sorts of manners of preventing the video working while driving. Parking break sensor, gyro's that detect vehicle motion, gear selector sensors ect. This is law that they have this prevention built it. They are tamper proof, meaning, if you try to disable the built in prevention, it will prevent the unit from working.
None of these in-dash systems have a nice little button to allow you to watch video while moving if you feel like it