Nice and strong argument.
Lets now imagine that magical world we're talking about.
No guns whatsoever.
You think the guy would have killed his girlfriend some other way? knife? archery? poison? Maybe but I think less likable.
For him to commit suicide? Probably, jumping of a bridge, etc.
How many deaths could be avoided?
Would those deaths be worth to be waiting for a police state?
We would never know...
If someone wants to kill someone bad enough to actually carry the act out, they will use whatever weapon is at their disposal.
OJ did just fine killing two folks with a knife.