What do you mean by “allow you to kill a 3rd party”?
Like if rioters are breaking into your window and start trying to pull you out through it, then you floor it and kill someone else in the crowd who wasn’t actively breaking into your car?
This is something that’s going to vary from state to state, but ultimately it will be a case by case decision where a jury will decide if the use of deadly force was reasonable.
You will be judged based on other’s perception of the events, not based solely whether you yourself thought you were in danger or not.
So, someone trying to “drive slowly” through a group of protesters would probably be found at fault, while a car that was stuck trying to wait patiently suddenly having a Molotov cocktail thrown on it would be judged differently. Even then they will need to consider whether you could have just gotten out of your car and run.
