Firearms account for approximately 18,000 suicides annually in the US and approximately 10,000 homicides.
So, even if we lump in homicides with your suicides AND assume homicides are committed by legal gun owners (which most times they are not): 28,000 is 0.035% of 80 million gun owners in the US, which means it is NOT the "primary purpose of owning a gun". It in fact accounts for a MINISCULE use of firearms.
The primary purposes for owning a gun - BY FAR - NOT EVEN CLOSE - are self defense and sport (including competitive shooting, recreational shooting and hunting).
Also, I suspect that you are misinformed on what an "assault rifle" is which is not your fault since the media spreads so much hysteria and disinformation...
An assault rifle is a marketing term. These rifles function EXACTLY THE SAME as semiautomatic hunting rifles. The only differences are: they look more menacing, have accessory rails and a different grip. You can buy a wooden rifle - not considered an "assault rifle" - which fires the EXACT same caliber bullets, at EXACTLY the same rate with EXACTLY the same capacity.
Also, while you did not mention it here, let me also bring up "high capacity magazines" since a lot of "anti-gun wackos" (as I'll call them) bring these up for argument. The difference between shooting a 30 round magazine and three 10 round magazines is about 4 seconds. With just a small amount of practice, anyone can reload in under 2 seconds.