Statistically, because of course guns have not been around for 10,000 years, the average gun in America will be used in a homicide once every 10,000 years. Thus to claim that their primary use is homicide is clearly false. Thus you need to come up with a better answer. In fact they are not designed to kill but to protect, those that are not designed for hunting or target shooting, and that is what they are used for as many as 3 million times a year.
Accidental gun fatalities are at an all time low, despite gun numbers being at an all time high and a much larger population and much more liberal gun laws.
Why do you care what method people use to commit suicide?
Gun suicides have trended down over time as well.