The problem you have here is one of threat. If this person calmly walks towards the door, without making a threatening move towards you, will you just let them leave? You'd be crazy to try to physically restrain them, but you just said you wouldn't shoot them in the back.
Granted, Its a tough one. It's also one that I would say is a very unlikely situation.
Let me throw this possiblity out using your scenerio:
he calmly walks to the door without making any threatening moves towards me. How do I know that the instant the line of sight is broken, this person uses this opportunity to draw a firearm and attempt to shoot me. Afterall, chances are I've got a good description of him for the police. In my job, I have to watch 8-10 hours of news every business day. The chances are FAR more likely that a criminal would take action or take the opportunity I put as a possiblity than do nothing but calmly leave.
Theoretical arguements only have value in a lab experiment. In life, there are FAR too many varibles. And as I pointed out, the threat level is dependent on these varibles, your analysis of that threat level, and the potential of YOU being the one shot.
I submit that ANY situation where someone is on YOUR property and STEALING your possessions should be considered a threat and ANY action beyond remaining still with hands visible MUST be considered a threat. The person has already shown a disregard for the law, why should I believe he respects my life or the laws protecting it?
In the scenerio that you mentioned about the person moving towards the door, I would inform that person very sternly to remain in place and that any move to break line of sight would be considered going for cover to shoot me, and therefore a threat to me.
Rather than berate people who would defend their home and property, why not place the blame ON THE CRIMINAL? It seems we are adverse to do that in our current world. If someone breaks into my property and is stealing from me, the burden of responsibility falls upon HIM. I will, of course, inform that person that anything other than doing as instructed will be considered a threat. The choice of doing something stupid and the consequences of such are HIS responsibility.
There is precident for this action seen every day. LEO's routinely insist on having complete control of a situation and consider any action other than compliance as a threat. Letting guard down as caused several LEO deaths that they didn't see coming. Why would I be held to a higher standard than a trained LEO?
For the record, I am not some Keyboard commando like I've seen referred to in this thread a couple times. A lot of people try to imagine what they will do, and often do very differently than what they type. While I am not in LE, I HAVE been in a couple situations where what I type had to face the acid-test of reality. The most recent was my home being broken into on December 6, 2006.
There was a very significant chance that the criminal was still in the house when I got there. As it turned out, he wasn't. The responding LEO and I arrived at the home at the same time and my wife was waiting in her car. Because there was a chance the criminal was in the home, it had to be checked. Because I had my Vector AK-47 underfolder with me, the LEO asked me to help him sweep the house.
When we went in, The LOE yelled for anyone that was inside to come to the front room with his hands on his head. He yelled to inform the potential criminal that not being in that front room with hands on head would be considered a threat situation and we would act accordingly. I was given a few quick instructions regarding moving room to room and what I should do if faced with a threat.
To make a long story longer...
The LEO with a Glock 17 and me with a AK swept the house room by room covering each other as needed. The criminal was not there.
While this seems anti-climatic, it was a valuable experience for me. I was placed in a position where I would have to act based upon a threat level. I was put in a position where theoretical arguments are meaningless, and where you had better be ready to act.
After going room to room through my own house not knowing if I would be walking into a gun pointing at me, I passed being a keyboard commando.
John