Guns are whatever that you make of them. You can use it as an assitance in a robbery of a bank, or you can use it as a defensive piece of metal. The intent of the item used is what is being discussed, you dont have to shoot the person dead, at the very least stop him from casuing more harm.
Murder has premeditated malice in it, when you are defending yourself you dont think ahead. You dont know theres going to be someone breaking in your house else you already call the police. Its not hypocritical at all, its just looking out for yourself when someone that does threaten you, so you arent using sticks and stones against a gun.
In that same analogy, why have an army when we are for peace?