Turning off the ignition may deactivate your airbags* which could make a bad situation worse.You would be much better off attempting to shift your car into Neutral first.
* This was what made the GM Ingnition switch problem so deadly. The engine shut off (taking power steering and vaccuum-assist braking with it) and the airbags deactivated making any subsequent crash less survivable.
You're right that shifting is better. That is a pretty terrible failure mode for airbags, however. How much would it cost to put a big reliable capacitor in the airbag circuit, to keep the power on for 30 seconds? A dollar?
* This was what made the GM Ingnition switch problem so deadly. The engine shut off (taking power steering and vaccuum-assist braking with it) and the airbags deactivated making any subsequent crash less survivable.