“Guns are only for killing” is a gross oversimplification. Guns are designed to launch a projectile. Many guns were designed primarily to shoot animals and people. However, many guns were made specifically to shoot holes in paper. We, not the gun, decide what and when we shoot.
Guns and the people who use them have the potential to hurt, injure and destroy. True. Therein lies another utility of a firearm. Sometimes some people need to be shot. Why do you think that we have justifiable homicide statutes?
A violent felon would not be deterred if there was not a potential to kill or injure them. Sometimes, a citizen or cop is forced to actually employ the countervailing use of deadly force to save an innocent life. Seven out of 10 people survive a handgun wounding. The intent is to stop their immediate aggressive actions, not necessarily kill them.
Knives are made primarily to cut. Whether it is a steak, tomato or person is up to the user. So it is with a gun. The utility of both tools outweighs their abuse.