I like to frame it thusly: Agents acting on behalf of a hostile foreign power slaughtered Americans on our own soil, and the Democratic response to this is to disarm Americans of the best available means of defense against such attacks.
I always wonder, how exactly do you think a massacre like the French one would have played out had the citizens been armed?
I live in a gun control country, so I have no idea.
If you go to a music event where you expect hundreds of others to be dancing to a metal group, do you carry a loaded weapon within easy reach with the safety off?
Do you keep exact track of who is there and what they look like?
Are you ready at a moments notice to drop, draw and start shooting?
Because even if the first one were true, I expect the event to go like this.
1: People are dancing to loud music, but now 10% carries loaded weapons
2: Terrorists come in and open up with automatic weapons without warning.
3: Those carrying weapons that are not immediately killed draw and start looking for people shooting.
4: They see each other AND the terrorists but don't know who is who so friendly fire will occur, hitting even more random innocents.
5: The same amount or more people will die.
In fact, the only time where I can possibly imagine a gun saving you from a criminal would be during a burglary (and even there I imagine the chances of loss of goods going to loss of life increase a lot). Every other time a criminal or terrorist will have the drop on you. Attempting to draw will probably cause a criminal to shoot you, and the terrorist will have shot you before you even realize it is happening.
While the argument that in a gun control country criminals can get guns is of course true, the counter argument that it is a LOT harder and that random joe who wants to start killing tomorrow cannot get guns is never mentioned.