I'll answer your last question first. The officer acted responsibly. Not heroically. I don't think there's any ideological conflict about how to deal with active shooters.
Now, as for your larger question: the first thing we need to do is chuck overboard the silly notion that there are so many guns out there, we can't do anything anyway. The reality is that gun restriction, not gun eradication, is a realistic and effective goal.
Case study: Australia. Gun culture, lotsa murders, you know the drill. Then one fine day, they passed a near-total gun ban. There was bitching. There was griping. There was moaning. Then the murder rate dropped by 93%.
The Second Amendment confers a collective, not an individual right. It is explicitly worded to that effect. The Supreme Court was dead wrong on the matter, which is part of the present problem.
But entirely aside from whatever restrictions, mild or draconian, we may wish to impose, there's another, more fundamental change that must take place. We have to de-romanticize and de-fetishize guns. Why is the hero of every movie the manly man who guns down 137 bad guys (never missing even once)? Why is every cinematic (and TV) crisis solved by Gun Man Ex Machina bounding onto the scene? And why does every Walter Mitty keep a gun in his nightstand, lying awake and fantasizing about getting the drop on some foul miscreant and filling him with holes, with the happy result that his wife will have sex with him (Ooh, my hero!!"), when the most likely actual event is, he'll shoot the neighbor's cat?
My reaction to firing or even touching a gun is simple revulsion. However, I'm in the minority. For far too many people, such thoughts give them an erection. What do we do to cure that? I don't know. Maybe publish full-color photos of the bodies of schoolchildren slaughtered by some asshole? You know, blood, burst skulls, gaping holes in chests, arms blown off? Would THAT do it??
The iconic image of guns isn't John Wayne; it's the director of the funeral parlor. It's fucking well time we realized that.