What difference does it make? If someone has decided to shoot someone else in a church, a law either allowing or prohibiting him from bringing a gun into church means absolutely nothing. There's already a law against shooting people. Anyone willing to ignore that law isn't going to be deterred by a law that says he can't have a gun in church.

As for laws specifically allowing guns in churches, I guess the idea is that if some whacko does commit an assault, armed congregants will be able to take him down. Well, unless those armed congregants are trained police or military personnel, the odds of someone being a hero versus accidentally shooting an innocent bystander are probably about 50/50. Maybe it would be a good idea to encourage appropriate people to have guns in churches, but allowing every swingin' dick to do so is as likely to result in tragedy as heroics.