To an extent, she is correct in that there are some who will still commit these crimes (or acts of treason) regardless, but clearly the ability to interrupt the mass killers by shooting back will reduce the body count, i.e. save some lives.
The point of what I'm saying is that arming people, while that's a good idea and is for self-defense -- is simply not going to stop these kinds of mass killings. So people shouldn't kid themselves into thinking that this (i.e., arming themselves) is the answer to these kinds of mass killings. It's not.
Now, I'm not inclined at all to go in and start shooting it up with a bunch of people I don't know, just because I'm mad or I got divorced or I lost a job, or I'm mad at the world -- but -- just technically speaking -- it would be easy for me to go into a place and probaby kill ten people in short order without the chance for someone responding fast enough, even if everyone of them was armed. I would has surprise at my disposal and I was be ready and I would have the necessary weapons to carry it off in short order.
Now, perhaps this kind of person is nuts (most likely or has "snapped" [as in the Tualatin, Oregon shooting or the Orlando shooting]) and is will to be killed in the process -- but a bunch of other people are going to be taken out before anyone can respond.
And the point that EVERYBODY ELSE is making is that while “THE ANSWER” to these kinds of killings (if by “the answer” you mean some kind of solution that will prevent them from ever starting) DOES NOT EXIST, having a population that includes armed law-abiding citizens is a better solution than relegating the entire population to a bunch of unarmed victims.
If someone is determined to go into an office and kill two or three specific people (plus anybody else who happens to be in the way) and then kill himself, then that group of people is probably going to be dead LONG before law enforcement can arrive. The best chance that anyone in that group has for survival is if one of them other than the intended killer is armed. For that group of intended targets, armed self-defense is the only answer that will save lives. Will it prevent the first shot? No. It may not prevent the second and third shots either. But it might prevent the fourth and fifth shot, and all the other shots that would have taken innocent lives before the cowardly murderer completes his rampage.
And there are literally HUNDREDS of examples where this has been the case.