Was I incorrect? Do you have some case law that shows that I'm incorrect with my conclusions? I'd honestly love to read it if so.
There are fiftyone sets of laws which might be at work in the United States, so it's hard to give an exact answer. Let's go back to the history of the quotes. It started with...
No one is responsible for your safety but you.
I am not responsible for your lack of safety even if my guns are stolen and they are used to kill you.
As a statement of personal philosophy, that's all well and good. As a legal statement, he's wrong. You appear to be siding with Xulld.
Your similar statement was...
Both of those situations are caused directly by someone's actions. If someone breaks into my secured home and takes my gun and shoots the neighbor, I am in NO way responsible because they were secured in my HOME. Someplace that the bad guy shouldn't have been to begin with. Plain and simple.
The key legal question is whether you can be held responsible if someone takes your gun and shoots the neighbor. The answer is that it depends on the exact circumstances, and the laws of your state.
In general, if they were secured to the state's standards (not your standards, but the state's standards) you are probably safe. If, on the other hand, you failed to follow the laws of the state, then you could very easily be held liable.
It's a bit like swimming pools. If a neighbor kid trespasses on your property and drowns in your pool, are you responsible? That's an easy one. Yes...if you failed to secure the pool in accordance with local and state regulations. Trespassing children are a foreseeable consequence and you are responsible for failing to take the required steps to mitigate the danger. If you try to use the "but he shouldn't have been there in the first place" defense, you will lose. Plain and simple.
And that's what I was getting at with your argument about your guns. If they are secure and you follow all laws, you're probably ok. If not, then you seem to think that "he shouldn't have been there in the first place" will somehow protect you from liability. Good luck with that.
ETA: Here's the first hit from google with the phrase, "liability for stolen guns".
http://www.nola.com/crime/index.ssf/2012/11/how_liable_is_the_owner_of_a_s.html
5 second summary: You could be held liable, but only if he accidentally shoots your neighbor. If he does it on purpose, you're ok.