We are not talking about a child that is lawfully present in a house getting your gun, we are talking about a thief breaking into your house illegally, stealing a gun, and the owner being responsible for that.
I am well aware of the law in regards to children and firearm safety.
The narrative being presented is that any method for securing if defeated was insufficient.
Just imagine if we used the same logic for any other property. That can of gas in your garage can kill. Should we hold the owner responsible if a thief breaks into their house, steals the can of gas, and uses it to kill the family next store in an arson fire?
No of course not.
In terms of the gun, it depends whether reasonable steps have been taken to secure it.
If the gun has been taken from a secure gun storage device then the homeowner has taken reasonable steps to secure it. If it has been taken from a desk drawer or picked up from an open surface then it has not.