Well it isn't the security that seems so absurd to me, its the idea of that person being armed with a lethal weapon that is so goddamn retarded.
I mean they don't let ME carry mace or anything, let alone a damn GUN.
I think its ridiculous that this woman was allowed to carry a loaded weapon around IN A CHURCH no less, despite whether or not it saved a few people from ONE nutball with a gun I still think its stupid AND dangerous.
I think you're being a little naive.
Obviously there are two types of security: armed and unarmed.
Unarmed guards are mostly hired when there is no real expectation of anything happening, but you want to reduce the possibility (as in no one was probably going to do anything anyways, but they definitely won't when there's a person there), as well as making the people around feel secure and know the property (in this case a church) and so on.
Armed guards exist because, well, shit happens. If you're carrying or watching money or anything of great value, or if there is a large event where there is a percieved chance of some nutbag coming out and being violent, it makes all the sense in the world for there to be an armed guard. In this case there had been a shooting at a nearby mission area, and they decided the chances of them being a target was likely enough that they wanted one or a few guns on the property.
Besides, given her background in law enforcement, I doubt that she wasn't both licensed and experienced in the use of handguns.
But yeah, saving lives is stupid and dangerous.