A gun would not have made a difference, it is insane to think otherwise
It is probably correct that a gun would not have helped in this peculiar instance, but there are special factors involved--Primarily the previously-mentioned hero, Greg McKendry. From what I know of the events, without him the tragedy would have been much worse. Heroes with enough balls to stand up against a shotgun while unarmed are in extremely short supply. Minor heroes brave enough to return fire when armed are much more common. I think I could be in the second category under some circumstances, but I don't see myself up to Mr. McKendry's stature.
I have yet to hear of a legal civilian armed defender who has made a situation like this worse.
The Unitarian church has an anti-gun policy. It is possible that this influenced the shooter, (whose name will remain unmentioned and unremembered here if at all possible) or at least its choice of targets--These types of shootings take place disproportionately where guns are not allowed. (Which brings me to....)
You are blaming the victims
The blame lays 100% on the slime with the shotgun. There was nothing the U/U church did to deserve this--Neither their gun policies or their gay-rights policies are to blame. Additionally, this sort of thing is so rare that absent a specific threat, specific preparation is not warranted.
It is irresponsible to have guns around children
In the presence of children, guns must be either securely locked or under the secure, direct and continuous control of an adult. Most holsters qualify. Most purses do not. In a huge majority of children's gun accidents there are obvious contributing factors, including a criminal living in the house, a significant case file with Children's Protective Services and/or domestic violence. Injuries are rare, injuries in normal, law-abiding middle class homes are extraordinarily rare.
You are using a tragedy to further your agenda
"After a shooting spree, they always want to take the guns away from the people who didn't do it."--William Burroughs.
This tragedy is no exception. The shooter used a hunting shotgun, apparently still equipped with a magazine artificially limited for hunting. "We aren't after your hunting guns"--What restrictions would have prevented this, without severely infringing the rights of the law-abiding? There is good and evil associated with guns. The good outweighs the bad, even if it is not as visible.