Cars offer a great benefit to society so we are willing to forgo a substantial number of car deaths in order to have this advantage. Private gun ownership, however, offers negligible benefits to society other than to farmers livelihoods.
Of course, if someone has a strong enough conviction to do so, he will kill using whatever weapon he can lay his hands on, but if that weapon happens to be a gun he may kill 10 or 20 people given the opportunity, versus the 1 or 2 he would have killed if he had only a knife or a sword.
You'd be hard pressed to find an example of umpteen killings being made by one man wielding a blade. And I really dont think you can read anything into the fact that, in those two examples, the gun man killed himself but the blade attacker didn't. Ending your life with a blade is much harder, and very painful compared with a shot to the head!