I don't own a handgun, and have no intent to get one. I do have a shotgun, which I use to protect the chickens from varmints (not very effectively, I might add), but I know that's not what you're talking about.
In the church I pastored prior to where I am now, I was aware of a few people who carried during our Sunday morning worship service, including one of our sound techs. He was in law-enforcement (although obviously not on duty while at church), so I knew he was well-trained. He never brandished his gun -- I don't recall if I even ever saw it -- and most people in the body had no idea he was carrying. He certainly didn't go looking for trouble, and I don't think it would be fair to characterize him as "living by the sword."
However, if someone had come into a service and started shooting, I'm certain he would have done what was necessary to stop the shooter. And I have no problem with that. I know that scenario is quite unlikely, but it does happen, however rarely.
Although I am not interested myself in preparing for that kind of situation, I do not believe it is wrong for others to do so if they choose.