Seems like it could be a double edged sword though. Don't allow firearms and the store is liable. Allow firearms and they could still be liable if another customer ended up causing harm with a firearm.
The other problem with this type of suggestion is that it can snowball. So imagine you park your car in a parking lot of a business and it gets broken into. Is the business responsible if it didn't have a security cameras? What if it did have cameras but no security guards? What if there were security guards but the injured party says there weren't enough? I don't think we should take steps to an even more litigious society.
You say that the accident was foreseeable but that's not a good example because the store is creating the wet floor, the store isn't creating robber.
I have no objection to voting with your wallet, if a store has a sign saying no firearms allowed I will choose another store if possible.
Wrong.
If someone walks in and starts shooting, and the people were allowed to be armed, they'd have a chance to fight back. If they choose to be unarmed, that's not the business' fault if they were allowed to carry there.
The guy who wanted to commit murder would have entered armed with a weapon regardless of the signage and policies. There's no liability for the business in so far as what one criminal decided to do.
Unless you can prove the gun-friendly policy had something to do with the criminal act of that one individual, then the business is not liable.
Making his customers sitting ducks against their will when the criminal shows up -- that's something that can have foreseeable consequences.
It's not a difficult concept. Maybe you'd like to further explain this double-edged sword theory of yours.
As for your poor analogy, courts have ruled in many cases that a business was liable for car break ins and damage in spite of signage saying you're parking at your own risk, company not responsible, yada yada... It all depends on the state's laws and the circumstances. Disclaimers cannot counteract negligence or failure to take reasonable measures to safeguard parking lots and garages especially if break ins and car theft are common in that lot/garage.
On top of all that, there's a massive difference between property loss and injury or death when it comes to liability. That includes amount of damages.