About the only thing I can add to the other responses is this:
it seems like someone who was insane enough to kill dozens would not be sane enough to think "gee, where are the guns," yet look how often places with a no-gun policy are attacked, and how much plotting the crazies go into to make sure they can kill the maximum number with the minimum risk. (since they generally shoot themselves as soon as someone with a gun shows up and takes a shot at them, I really can't understand it)

Then look at the church shooting-- where the shooter thought that there wouldn't be guns, because there hadn't been before; they'd asked for volunteer armed guards.

((I'm tempted to try to argue your interpretation of the second amendment, but I'm dang near sick of it since I'm listening to the arguments being hashed and rehashed.))