I live in rural north Idaho, which is definitely one of the places you're referring to, and simply saying you feel threatened is only going to get you so far... Your assertion that the random person at the door was a threat has to meet a "reasonable" criteria. A reasonable person would have to feel threatened under the circumstances.

Putting a .30-30 round through the front door when somebody rings the doorbell is a total crapshoot. If it's the pizza guy or FedEx, I'm 100% fucked, because nobody's going to buy that they were being threatening in any way.

It's not as simple as you're suggesting :)