No, these sorts of people would not carry a gun even if it were legal. The terrorists attacked the most ‘boho’ part of Paris, it’s metrosexual city!
And. often times concert venues search you anyways for weapons. Inside the concert venue wouldn't have mattered.
That being said, if you are going to have a weapons free place as a business, you should be mandated to have armed security.
My wife's hospital has the stupid azz 'No Weapons' stickers on the doors. Pisses me off.