I've been thinking about this for a while now and have finally come to a consensus on my feelings and the facts. The US gun culture is creating a climate that makes it easier to purchase civilian weapons than it is for terrorists to import true weapons of war like were used in Paris, France. It's nearly impossible to buy a gun in France, so the terrorists purchased and smuggled in full auto AK47's. If you're already smuggling weapons, you might as well include some mines, grenades and incendiary devices, right?
Let's face it, a Glock is far less dangerous than an RPG or many other weapons out there. If they are going to have to import their weapons, I'm sure those will be far more potent than what is currently available to radicalized US citizens.
The gun culture of the US continues to save lives, even without arming the good guys. With that being said, carry your darn gun! All the time, and be ready to use it when you must. Where I live those pesky No Guns signs carry no legal weight, so I ignore them, just like the criminals do.