JayCee wrote:Also FWIW the word should be defuse, not diffuse. You're removing the fuse fro ma bomb, not misting a plant.
I like your illustration 
Seriously, though, referring to the second situation you mention, I think you'll have a very hard time convincing the police and DA that shooting him (or her) from a vehicle (moving at 70 MPH, no less!) was your only way out. Even if you could convince them that deadly force was necessary, they'd probably get you for reckless endangerment or something because (as somebody else already pointed out) there's a high chance that something very bad will happen to others on the road. Then, since this would almost certainly* go to trial, you'll have to convince twelve people who probably think that guns are only for cops & criminals to let you off. Even if the driver was a Bad Guy (and not just letting his kids watch Finding Nemo on the way to grandma's house), and even if he was in fact out to get you, I think you'll be unlikely to succeed because even if nothing else, you could've pulled over and given the driver a chance to go on his merry way. A lot of the laws are written in terms of "what would a reasonable person think", and I doubt twelve random people would see it that way. So now you're going to jail for a long time. How long? Well let's say you manage talk the charges down from "murder" to "involuntary manslaughter". Then you're looking at up to twenty years. That's twenty years of being in a dangerous environment without the means to defend yourself, plus you won't be able to protect your family, either. And it's a felony, so when you do eventually get out, they won't give you your gun back, nor will you be able to buy an other one, nor will you even be able to vote for people who want to get those laws changed.
I'm not telling you not to defend yourself if you really do know for sure that your life or the lives of your loved ones are in imminent danger, but perhaps given the potential consequences, you should reconsider what it means to "know for sure".
*I think. I am not a lawyer, nor do I play one on TV, nor did I stay at a Holiday Inn Express last night.