The old movie theatres had two points of entry and we were still able to sneak in as dumb kids.
I think some of the on premise security stuff could help and I'm all for whatever helps.. but single entry is like treating cancer with some vitamin C... it may have some psychological benefits and may do us some good but we still have cancer. I'll take the vitamin C... but I still need the chemo.
Schools should be more safe than some community buildings... but if it isn't schools these idiots will shoot up churches, movie theatres, concerts. We can't confiscate all the guns but you can make it harder to get them. If someone has to get a gun illegally or make it (i guess this is a thing?) it will be a barrier to the crime... and I think that has to be the largest focus.
I also think mental health stuff should be at the forefront here. My experience with my daughter and her mental health issues has been eye opening. Schools, teachers, have been really hit or miss in being helpful and the level of effort we have put in has been a lot. I can't imagine if my wife was a working single mom or if we weren't vigilant parents that she would be getting the help she needs.