This will be for some court to decide. Someone will get shot in a palce where guns are not banned,and if the jury awards a bunch of money, the insurance on all such places will increase.
Or perhaps someone will sue for banning guns and someone will sue for THAT being negligent. Then they will stop banning guns.
This really does not work .
Every shooting is one or the other of these, and there isn't a stampede into court.
If someone wanted to sue on the basis that there was no ban on guns and there should have been , there will be a burden of proof for them , that such a ban has a reasonable expectation of reducing the risk a reasonable amount.
So that a reasonable authority has a reasonable responsibility to ban.
Good luck on that.
Starbucks has tried this one way and then the other , no suits either way.