Was going to say, I wouldn't be surprised if someone could win a lawsuit based on "The owner should have done a better job securing the weapons." I'm not in agreement with it, but crazier things have happened.
It would be a tough case to win. Basically explained, there are four elements to every tort (personal injury, for those who don't know) claim: 1) a duty; 2) a breach of the duty; 3) causation ("but for" cause is the basic principle); and 4) actual damages/injuries.
This would require either an actual legal duty, or a jury believing a duty existed under the circumstances, to secure guns in a manner that a thief couldn't get them. It would also require a finding that the theft of the guns was the "proximate cause" of the plaintiff's (presumably, the person shot by the stolen gun) injuries.
That latter issue, however, has become more blurred as time has gone on - juries in all states except Maryland and North Carolina are now allowed to consider comparative degrees of fault. What that means, is that even if the jury thought the thief/shooter was 90% at fault, they could still slap you with 10% of the fault (and of the verdict) if they thought that was your contribution.
So, all in all, it would be a tough case - but that doesn't mean it couldn't be won. Especially since civil juries generally only have six people on them, and they don't have to be unanimous - majority wins.
But, for all of you who own guns and who have enough assets to make a lawsuit against you worthwhile, consider this issue.
I say that, and mods feel free to edit out this part of my post or to delete this post in its entirety, because - and this is speaking historically - activist groups have traditionally turned to the courts and/or juries to force change in that manner when legislative reform hasn't passed. I'd hate to see one of you become the example that sets the "social standard of care" for gun storage and/or ownership.