If the horrific case of a family being killed is the one Bambi posted last week. i followed his link and read about that case. First off it was from back in 2007. One of the worst crimes in Connecticut in recent history. Not some sort of regular occurrence. A significant enough crime to twice alter the legislation to eliminate the death penalty in CN. Not the kind of rare awful crime you base your laws and personal behavior upon.
Further, the police were on the scene. They had the mother go to the bank to withdraw money (a poorly improvised robbery plan) where she alerted bank staff her family was being held captive at gunpoint. The police set up a hidden perimeter, and let the one perp and the mother return into the house. Then it seems the police dawdled while the two criminals raped and set the women and house afire.
So trained good guys with guns (police) were on the scene and failed to stop things. The husband was bashed in the head with a baseball bat while sleeping on the porch. So a gun wouldn't have done him any good. And likely the mother wouldn't have had a chance to react and get to wherever a gun would be kept before the home invasion got underway.
Basically there is no way to stop somebody intent on killing/shooting another person. Police and armed citizens can't be everywhere and always at the ready.
What I read didn't mention drugs, but the random violent behavior sure seemed like it was drug-fueled mayhem.
To recap the case was from over a decade ago, basically a unique case of violence and depravity for Connecticut. Cops were aware and on the scene and failed to intervene in time. A home weapon likely would have been useless/inaccessible.
Hard to see any lesson that should be learned, except maybe local police need more training for such situations. The idea that one should fear this happening to them or change their behavior/lifestyle due to this one horrific incident is absurd. Granted you can probably dredge up more randomly selected murder victims, but not that many