In general, I think vehement gun ownership relies on a level of hubris. Many, many of the individuals who end up shooting their families, friends, strangers and/or killing themselves thought they were the law abiding, non-violent citizens. It turns out that they were......until they weren't.
I guess I just know the depths of sadness, anger, and other powerful emotions that can overtake myself and others. I struggle with depression. Anyone like me should never have a gun in the house. This is extremely unwise. Even if I didn't struggle with depression, how am I to know if ones of my sons won't when they are older? I know someone whose child killed themselves with a shotgun. Why was the gun in the house in the first place? I never got the whole story and wasn't going to ask, but I really, really hope the daughter obtained the gun herself and they didn't know. She had struggled with depression for years. A gun should not have been anywhere near her.
The massacres are thankfully less frequent than the tragic cases I outline above, which happen weekly, even daily, all over this country. They just don't make the big, front page headlines. And someone above also brought up how many children in this country are killed yearly by unsecured firearms. That's the biggest tragedy of all.
As far as how I deal with this personally, since clearly I can't do anything about all the people around me who have guns, is that I know that my and my family's likelihood of becoming victims of gun violence is dramatically lowered by the fact that we ourselves do not have guns, our extended family does not have guns, and by and large our friends do not have guns. We could certainly be unlucky and be in the wrong place at the wrong time, but most gun violence either occurs in disadvantaged urban areas or in families with guns.