First, in the interest of full transparency, I did not read all of the posts on five pages, I skimmed them and read the ones I thought looked interesting.
There seems to be a discussion in some circles of what the true responsibility of an armed person is in a case like the school shooting in Parkland. In my opinion, it differs by the person and why they are carrying. I carry as a retired peace officer. I no longer have any obligation to charge in to a shooting. But as Charles pointed out, some of us are wired to run to the sound of guns and there is little doubt in my mind that, assuming I was there for some reason, I would go try to engage the shooter. I doubt anyone could find fault in me if I did not do so though.
If you have an LTC, I believe you have no obligation to defend anyone else other than yourself. I would not find any fault in any LTC who did not charge in, and would consider the ones who do when not required to be heroes. You are just wired that way, I guess, and I have no problem with that.
A police officer on duty has an obligation to charge in. In this case, I agree that it is not his being a hero, but him doing the job he is paid to do. I never agreed with the secure the perimeter training we received in the past and am glad studies after Columbine said to do otherwise. The ALERRT program at Texas State has professors who researched this and say the best way to end a shooting is for the first responders to get in there and challenge the shooter. In most cases, the shooter will suicide rather than face the police though this is not a guaranteed response. The shooter might really shoot back at the police and the first responder who goes in might die. But he saves lives while doing so even if it is just by distracting the shooter while more of the victims get away.
And one of the thinks that bothers me right now is the news coverage all focusing on the deputies who did not go in. We are missing the chance to honor a true hero. There was a man there who was not armed and was never expected to respond to a shooter the way he did. But the football coach, who helped out as a part-time security officer on campus, knew what he was doing and put himself between the shooter and students. Aaron Feis died while being a hero. I don't want us to focus on the cowards and not remember to honor the true heroes.