No, there really isn't... In what world would every person in a single, loud, crowded room be able to have a gun on them? That scenario is unrealistic, and thus does not serve as a good counter-scenario to the one that was presented. Regulating guns is realistic. Allowing every single person to have one on them at all times wherever they go is not realistic.

That's pretty the same thing as saying less people could have died in 9/11 if they all had fire-resistant suits and oxygen tanks that would allow them to walk through the fires in the building and prevent them from suffocating to death, thus allowing them to escape. Technically that's true, but is that a realistic scenario?