To each their own, but I'm thinking you're all smoking something funny along with a tinge of John Wayne fueled fantasy of how it's actually going to go down.
Having seen trained Infantryman freeze up in react-to-contact, 99% of you who have no formal training are going to quickly vacate your bowels into your pants (mostly figuratively but also literally in some cases).
Best thing for you to do is runaway and runaway fast as some numbnuts strolling around a shooting area with a weapon is liable to get himself shot by the professionals responding to the situation or by another numbnuts trying to be a hero.
The last thing I'd do is try to take on an active-shooter (especially one armed with a rifle) with a handgun and only engage in gunplay as a last resort.
I know my ideas aren't very heroic, nor fit into people's John Wayne fantasies, yet having done a thing or two in regards to using weapons under pressure and stress, it would be a rare man who can pull it off, especially when confronted with an unexpected ambush.
"Our contract called for 16 cases of rifles and ammunition for $10,000 dollars, not a machine gun...........That is our present to the General"-Pike Bishop