"But if the pro-gun lobby argues the rarity of such mass shootings as one reason (among others) against further gun regulation, it cannot then use that same rare mass shooting as an argument for wider gun carrying."
She doesn't say why, and her reasoning eludes me. So I can only justify having a gun by the number of times I use it to shoot bad guys? Is that what she means? And I don't think us pro-gun lobby types ARE arguing that. I don't carry to be a hero, a Walter Mitty. I carry to defend myself and any people I am responsible for. If I happen to help another innocent out helping myself then that is just gravy.