So you wouldn't attack him if you were unarmed, you wouldn't shoot him if you were armed, you wouldn't run away but you would roll up either? What course of action does that leave? Doing nothing. Which is exactly what happened in Colorado (and Virginia Tech). We don't have to wargame that COA to see how it turns out - it ends with at least 12 people dead and 50 wounded and the shooter having a smoke in the parking lot until the cops show up. Holmes didn't stop killing people until he decided to stop - the death toll could have been much higher. And you're main concern is not making it worse?
I'm not advocating a lone hero going mano a mano with the shooter. My problem is with the passive victim mentality that has pervaded our culture. I mean, here we've got a FIGHTER pilot who says he wouldn't do anything to stop the shooter even if you had a gun! The lone gunman mass murder scenario will cease to be a viable tactic once enough people realize that the only way to counter the threat is with a group attack. The people on Flight 93 figured it out instantly and changed everything we think about airline hijacking scenarios. The same thing needs to happen with the active shooter tactic.