The equal force idea is a nice one, but it doesn't work in reality. The idea that if someone has a knife, you can defend yourself with a knife is just plain idiotic. You are a law abiding citizen and he is a streetwise criminal. The facts of the matter are he is likely to kill you. It is your house, if someone comes in and threatens you with a knife I think you have every right to shoot the bastard in the face. You did not ask him to come and threaten you, so why should you have to defend yourself with the same level of threat?

That being said, if the threat is less serious (like a guy running off with a tub full of food as per the example above) then I don't feel that person deserves death. I guess what I'm getting at is I agree with proportional force, but I think this should be exercised in a manner of "if he threatens death (ie carrying a lethal weapon), you can respond in any manner that could result in his death" or "if he threatens injury of some kind (non-lethal) you may respond with injury (ie if someone comes at you with a 2X4 you could wing a bat at him or something)".

That is my opinion on the topic.