Because the statistics are against you for the vast majority of people who don't live in crime prone areas.
For people in relatively low crime areas, the mere presence of a handgun has increased their extremely low probability of death by an inordinate amount because of gun accidents. The probability is still low, but is vastly higher than if a gun wasn't present at all.
You can argue that this is due to stupid gun owners. Perhaps, but as technology folks, we also understand that you set up systems so incidents don't occur in the first place.
Every single person I know who has a handgun has at least one "accident" over 20-30 years. I know of zero who actually used a handgun against a criminal.
I will also point out, that I know a lot of people with rifles and shotguns, and those almost never have "accidents". I think I know of one over the last 30 years. Draw your own conclusions.
Obviously, if I lived in a high crime area or in a profession where it mattered, that's different.