Take another look at Tirecs list. The shooters are nut cases looking for death. They want to have an audience though, their 15 minutes of fame and most of them want to go down in a blaze of glory with all guns firing. Offering to engage in a shoot out with them is not a deterrent or a control.
However they are not really interested in being taken out in front of a locked door before they get to do any damage.
They are no different than suicide bombers.

Another sad point is that when you look at all these shooters in schools, churches and other public buildings most of them have already aroused suspicion in their communities because of their bizarre behaviour. Often they are shooting inside of their own churches and schools

Yes my philosophy of this is a bit different.
These people are obviously mental. They have a death wish and an imaginary score to settle.
I think just the fact they are not already in a padded cell is a security breach.

I do think of exclusion first. If I could I would not let them approach within range at all. If I could stop them at the parking lot I would. If the best I can do is the doors then so be it.
If they make it past the doors hopefully they made enough noise doing it that the people at the next point are warned.

If they have already been allowed into the crowd it is too late to prevent carnage. No matter how much of a quick-draw artist you are or how accurate you shoot they are going to get some shots off.

Benjammin caught the point about layers of security, and yes each layer has to be backed by another layer.
How many layers you get and how effective you will be at preventing incidents depends entirely on how much you are willing to pay for.
If all you are willing to pay for is volunteers in the congregation then all you are getting is the final layer of response.
Not only that, your final layer offers these nut cases exactly the response they desire. They want that big splashy exit. Remember when you look at Tirec's list what most of those people were after and how many of them suicided after they were stopped shooting.

As I said before, I have never been part of or responsible for a security team.
I have observed them and have done some of the set up for them though.
The most interesting security provisions I saw were for President Reagan's visit to Toronto in 1988. The most interesting part to me was the month of preparations along the Gardiner Expressway for his motorcade to pass.
Lots of layers there.
There have been a few times I wondered if Reagan was even in that motorcade at all, or if he was quietly brought in by a completely different route.

The visit of Her Majesty Queen Elizabeth, Prince Philip and Prince Edward to Victoria BC in 1994 was kind of interesting too.
It was a lot lower key, but every bit as intense.
The sweep of all underwater structures and hulls in the harbour was a surprise.
Both of these people are surrounded by bodies which are there to get in the way of a bullet or take down an attacker if they need to.
But the only way that should ever be needed is if all the layers before them have already failed.