Let's be realistic here. With the number of guns currently in circulation, a ban would only leave the law abiding unarmed. You could MAYBE have something different with a relative handful of guns out there, but not now. It's wishful thinking, and you would only make criminals out of a lot of otherwise completely law abiding citizens.
Okay, let's be realistic.
A gun ban in and of itself would probably be impractical, but putting limits on NEW guns would keep them out of the wrong hands.
The thing is, every time there is a mass shooting, it's not done with the gun that has been sitting in someone's closet since the 1990's. It's done with the gun that someone just bought, who slipped by a background check because the gun industry has so watered down that process it's impossible to catch them before they go on a rampage.
The NRA and gun industry WANT rampages. They sell more guns.