Some people buy guns to kill people. Even if you argue that most people buy guns to "protect their homes" (and if they are planning to own a gun, they're more than likely okay with shooting an intruder) there are still some people that buy guns with the intent of killing people. No mass murderer does so by crashing a Ferrari.
And also, your suicide point is irrelevant. People will find ways to commit suicide if guns aren't an option. These gun laws are not meant to prevent suicides, they're meant to prevent homicides and mass killings.