There has been quite a few successful self defense cases in Canada involving a firearm. People see this as a "petty crime" but how much crime is a home owner to endure? Theft of property and money in our society is actually a form of "Theft of time". We all have a finite amount of time to accumulate assets to provide for our families and our retirement. Theft depletes that amount always. At some point the victim can no longer recover from it.
I think you are viewing it wrong -- the issue isn't the theft itself -- it is the manner of theft - if there was violence or not involved in it.
If someone comes up and says "give me your wallet"
You have two COA's 1) Give the wallet 2) Refuse
If you chose COA 1, you cannot then act with force - unless the robbery doesn't stop there.
If you chose COA 2, the matter of what the robber does then relates to what you can do.
Civil society is based on the reasonableness of actions - and the minimum of force needed to accomplish a task.
Disparity of Force and Proportionality also dictate what levels of force can be used for Self Defense.
Down here case law exists on Disparity of Force justify the use of deadly force in situations where one if either dealing with multiple assailants - or a physical strength difference.
As well Deadly Force is Deadly Force - if you are attacked by a knife - you can use any means necessary to defend ones self, you don't need to use a knife - you can use a firearm.
*Again reasonableness - as an individual can't just shoot a guy at 100m because he had a knife and says 'I am going to kill you'.
Also if ones home is broken into when one is at home, most jurisdictions have found that a reasonable person would believe that harm up to and including the threat of death or gross bodily harm would befall them (or friends/family at the location) and deadly force can be used to defend ones self in those instances.
*Some US States do have duty to retreat laws - that basically make one withdraw if one can before deadly force is authorized - while in Florida one can shoot someone who is trying to take the hubcaps off ones car in their driveway, and have full Castle Doctrine.
**Some states have provisions that also block civil suits in that case - but not all.
The end result is no one case is identical - but I can pretty much guarantee claiming theft of time isn't an affirmative defense for anything.