So here's my equation for the leading cause gun deaths.
Gang membership (* some_rate) * gun ownship (* some_rate)
Gun deaths are mainly in cities with access to guns. DC had a measure of success in controlling hand-gun access (a hand-gun's only purpose is to harm another human being -- it has no moral concepts of "protection" nor "aggression"). Similarly, without high rates of gang membership, it's possible to have relatively few gun deaths with a high ownership rate. You can't restrict gang membership on freedom of assembly grounds (though the word "peaceably" might be a good legal loophole -- I've yet to meet a peaceful gang).
This is not very different from security at an airport.
Terror group membership (* some_rate) * weapon possesion (* some_rate)
Since we can't know the intentions of everyone on the flight, but we search everyone on the flight (while trying to minimize the first item as well).
Also, suicide is a funny thing. As it turns out, means is important. When England switched from gas stoves, suicide by gas went down while virtually all other methods of suicide remained constant. We could expect that fewer people having guns would prevent suicide -- common sense in this case is damned by empirical evidence.