As you might guess, the statistics do not support his decision:
"Guns kept in homes are more likely to be involved in a fatal or nonfatal accidental shooting, criminal assault, or suicide attempt than to be used to injure or kill in self-defense."
Well good thing I'm an individual adult and, after assessing my lifestyle and level of fire-arm responsibility, feel confident that I have control over these scenarios (not) playing out. I don't have any control over someone breaking into my house at night.
So, it can still be a net benefit to society to pass a law which reduces fatal accidents but increases break-ins. Also, I hope that you would sell your gun if you found yourself suffering from some symptoms of mental illness, or if you had children in the house. No one ever thinks that they will be the careless gun owner whose kid finds their gun, or the drunk gun owner who threatens their spouse.
Yes, I knew this. I have not bothered bringing it up with my dad, but may end up doing so in the course of making it clear that he can either have unsecured firearms or his grandson in his house and truck, but not both.
One cannot say something is regulated without admitting fault and adjusting when needed until the issue appears less and less.
Further major tragedies have happened, both directly with guns (Winnenden, 2009; Munich, 2016) and indirect (Berlin Christmas market attack with lorry, the theft of which was enabled by a murder with a handgun), but are just so much rarer, along with far rarer smaller scale tragedies - I've never heard of a small child playing with a gun and shooting themselves or a sibling in the nearly two decades I've lived here.
Speaking of which, that's going to be an awkward conversation with my dad and brother before bringing my kid to visit his other home country; I know that my dad kept a loaded handgun in his nightstand as of a few years ago due to very overblown fears of a home invasion.