Which would have stopped the TX shooter in what way exactly? Putting up a sign will stop a shooter? Wow, well I guess that didn’t work, did it?
If the folks in the church were carrying, they MIGHT have shot back. I know some people refuse to carry in church, or think churches are safe. Lots of would-be killers might think of them as gun-free, although they’d be in for a big surprise in some churches I know.