Franchisimo:
He says, I'm not gonna hurt you, just rob you."
In most jurisdictions, the definition of "robbery" is the unlawful taking of property from another through the use of force, or the threat of the use of force, coupled with the apparent ability to actually implement that force. So, it's impossible to "rob" someone if you make that person believe there is no threat whatsoever to them.
Let's say someone does indeed make such a statement. In fact, let's say they're not even inside your home, but attempting to steal your truck. You are certainly within your rights to go outside and attempt to stop him, using "reasonable" force if necessary. If he escalates the situation by not backing down and instead using force, or the threat of force, to take the vehicle, what started out as "theft" is now becoming "robbery". You would then be able to keep ahead of him in the amount of force used, up to and including deadly force if required, to protect yourself.
Now, let's say it got to the point of you shooting him, and he died. While it's true that many will say he "was killed over a truck" (or a wallet, watch, pizza, or whatever), the truth would be that he was killed because he presented himself as
ready and willing to kill for it himself. That is the crux of the situation.
There is no legal requirement (in most jurisdictions) to simply step back and surrender your property to anyone who is trying to rob you of it.