That obviously depends on the door. Do you really think your home offers physical security?
Locked doors are deterrents. Governments and lock makers do not assume/guarantee that locks are unassailable, they guarantee that they are unassailable for some unit of time.
Active shooter situations are usually counted on the order of minutes, and when you're dealing with minutes, locked doors certainly do matter.
You stated that locked doors were a solution to security when they are little more than security theater. They keep out only the people who would passively attempt to enter your home.
I am well aware of bump keys, and how easy it is to bypass locks. That's what the whole scandal is. Companies are guaranteeing their locks are good for a certain amount of time, and their locks do not live up to their guarantees. But again, we are not talking about my home.
I would also love to hear figures on how many mass murderers carry bump keys on them? How many shootings do you recall where a gunman gained access using a bump key, or otherwise picked a lock?
Again, the lock is a deterrent.
There's plenty of discussion of the roles of locked doors in these sorts of situations. here's one: http://www.npr.org/2013/02/15/172130144/would-more-secure-do...
You offer up locks as a solution to this problem and I'm merely pointing out that I think they are grossly inadequate.
Once someone decides they're going to take a gun and start killing people, it's non-trivial to stop them. That doesn't mean that we can't reduce the number of people they can shoot at and kill. That's where closing off the avenues that a shooter can take is effective.
And even if someone did wait for classes to let out, firing a gun and killing people at a distance is not easy. You start shooting at people, and presumably they'll scatter.
If, however, someone had a reason to break into YOUR house specifically(could be as simple a motive as you having a really expensive car parked in your driveway compared to the neighors), a locked door would be a laugably ineffective security measure, because he could get through one of your windows in just a few seconds.
Additionally the process of circumventing a lock requires time, effort, at least a little practice and familiarity with the tools, which most of these guys do not invest into their murder sprees. Whether a lock can be broken is a different matter from whether a lock will slow down an assailant unless the lock offers no resistance.
Some lock circumvention techniques take almost no skill, and no time at all. I've seen cipher locks that cost thousands circumvented by lightly tapping the housing with a rubber mallet or sticking a paperclip through a gap near the LED to create a short. I've seen people open locks with a piece of toilet paper or a key that was milled using a photograph taken of a key-chain on someone's belt from across a parking-lot.
Shooter has his gun(s) out, he approaches door, he now has to holster gun, get out bump key, focus on and fiddle with door, and once it's unlocked, open up the door, unholster his weapon, and then enter the door.
How many times do you think the shooter is going to expose himself like that? Does that feed into the fantasy of stalking people through the hallways shooting them?
If a shooter is using a handgun, well with just a little bit of practice, you can learn to draw a handgun in a fraction of a second.
Basically, I don't think it's a good idea to assume what will or will not be reasonable in the eyes of a mass-murdering lunatic.