Having undergone active shooter training (for unarmed civilians), I can tell you that responding to an active shooter involves more than just locking the door. You lock the door, turn off the lights, and make it look like nobody is in the room. If you can, you barricade the door to make it more difficult for the shooter to get in.
Active shooters have very little time to operate (the one at Sandy Hook had 10 minutes), and they look for easy targets. Even if an active shooter knows you’re in the locked and barricaded room, he’d likely rather keep moving looking for easy targets than waste time trying to get into that room.
(BTW, if a future active shooter were to read about this plan and modify his plan because of it, he would waste time looking in empty rooms and hiding places, and that would slow him down from finding easy targets, so I think there is minimal risk in sharing this info. )
The key to surviving an active shooter like this isn’t necessarily just making yourself hard to find, it’s also making yourself a difficult target so the shooter faces the difficult choice of spending time and energy trying to get to you or moving on to find an easy target.
I’m not one of the people you mention who are terrified of guns and are ignorant of the technical issues. I’ve handled guns and undergone training in how to use them, yet I will be the first to recognize that I don’t have the necessary training and experience to handle an active shooter. First responders undergo intensive training in how to handle those situations. They conduct supervised simulations, evaluate their performance in those simulations, and retrain repeatedly. Few civilians have that level of training, and any civilian who doesn’t have that training has no business messing things up for first responders, who might mistake such a civilian for an active shooter or an accomplice.
When you look at the few cases in American history where armed civilians had a role in taking down an active shooter, they were either off duty police officers, retired police officers, or retired military officers, and many of them chased down and apprehended the shooter after the damage was already done.
Oh, and everyone, let’s not forget that we regulate automobiles. In fact, I can’t think of a single consumer product that isn’t regulated in some way, with the sole exception of guns. Guns are the only consumer product I can think of that we don’t regulate.