“A gun in a safe is better than nothing.”
You might have a half second from the time the shooter spies you. Can you get your gun out of the safe and aimed in less than half a second?
If, OTOH, the gun were on your desktop, you might have the edge on the shooter.
Ms. Soto, a teacher murdered by the animal, had time to get a gun from the safe and put herself into position to plug the shooter.
What if a krazy kid takes your gun from the desk. You trust all the students to have access to your gun on or in the desk?