On the subject of mass casualty events:
According to FBI statistics, armed civilians were successful in 94 percent of engagements with active shooters. They stopped the perpetrator in 76 percent of cases and helped to mitigate loss of life in a further 18 percent (note: list below includes cases of police officers being rescued /defended by armed civilian in situations that do not fit the FBI active killer definition).
All recent terror attacks in the European Union were committed with illegal firearms that were mostly smuggled in from the Balkans.
Active shooters stopped by a civilian in the act (In the US, Source: FBI).
Approximately 2000 lives were saved by the engagements of armed civilians mentioned in the table above.
For individual level cases (robberies, sexual assault, attempted murder, and other violent acts that aren't considered a "mass shooting"):
Numerous agencies in the US have concluded that there are up to 2.5M legal defensive use of firearms cases each year. The lowest estimate has around 100K. This range is very wide for many reasons, the article addresses this question. This number includes cases where just the display of a firearm was enough to stop the criminal act. The general consensus from nearly all reputable studies concludes between 1M and 2.5M.
I encourage you to scroll through r/dgu (DGU = defensive gun use).
Also: "Gun Free Zones"
Police response times can be up to 20 minutes in some areas. In my hometown, it is 11 minutes. If someone is breaking into my house with a knife/gun/whatever and I call the police, how should I defend myself during the 11 minutes? Negotiate? With what? You have no negotiation power if you are at a disadvantage. You need to have something of greater power in order to negotiate with a violent criminal.
Do a test for yourself, look up what the police response time is in your area. Set a timer for that long and start it. Sit there and look that the timer until it runs out. 11 minutes is a long time to wait for police to arrive when there's an armed crackhead breaking through your window.
This isn't just me looking for reasons to have a gun, I am generally prepared for what I think I should be prepared for. I have two fire extinguishers in my home because the fire department can take up to 20 minutes to arrive. I have 30 gallons of drinking water, 2 weeks of food supplies (for 2 people), and 2 weeks of cooking fuel because I live in an active earthquake zone. I wear a seat-belt because car collisions are common. I have a first aide kit in my car to treat numerous injuries from deep cuts, broken bones, gunshots, etc. None of this is crazy stuff either. Fires, car collisions, injuries, and natural disasters are common. Violent crime is also common so naturally, a gun is the logical thing to have, in my opinion.
