Taking away the privilege of owning and using anything the vast majority use lawfully and responsibly because of the intentional unlawful use by one individual seems arbitrary to me.
I get your point of view, but police in NZ have been raising questions about increased gun violence and in particular increasing levels of semi-automatic and fully automatic weapons for (literally) many years.
These same police don't carry guns.
Faced with a choice between increased militarization of their police or an attempt to scale back ownership of certain weapon classes, they've taken the latter option.
Most countries seek to balance individual rights with societal considerations. New Zealand, for example, has been progressive in both indigenous and women's rights.
So, sure, you can paint this as knee jerk, or as ripping rights from lawful people. Much of the world doesn't view a healthy society as a group of individuals only, though.
It makes conversations difficult due to this constant balance, but it's why most of the first world falls a different way to the US on things like universal healthcare.