The club and the knife were most likely the first weapons developed in human history. Their primary purpose was to kill animals to provide food. By attaching a knife to a pole, as in either a spear or an arrow, the effectiveness of the knife can be extended. Then, some humans learned that they could use these weapons to take property from other humans. The most valuable and sacred property is life itself and once that has been taken, all other forms of property become available to the attacker.
If one human with ill intent is armed and another is not, it becomes easier for the armed one to seize the property of the unarmed instead of working to create their own property. The correct and ethical response to an armed threat is to arm oneself in order to protect life and property. In fact, in most cases, it is unethical to do otherwise. Enabling an unethical attacker to succeed, even through inaction, is not a wise course. Surely there are specific cases where the best course of action is non-violence, but these are exceptions to the general and must be carefully considered.
Knives and spears were adapted into swords with a primary purpose of close range combat functionality. Self defense required this, but again, ethical tools of human function were eventually also used in un-ethical attacks. The progression of technology continued to expand and extend the functionality of arms. Gunpowder was just another step along this path. While guns can be used as hunting tools to provide food, when attacked by other humans who are using guns, it becomes survival essential to defend yourself with guns.
The primary purpose of the 2nd amendment to the US Constitution is not to provide food or to protect sport, but to defend against the tyranny of big government and their ability to use military force. It is worth noting that the most heinous misuses of arms in history have been committed not by criminals but by large nationalistic military organizations.
Those who argue for arms control usually do not try to make a case for total disarmament, but rather want arms denied to the people and concentrated in the hands of government agents. As in the case of socialist economics, this can only work when the ethics of the government and their agents is flawless and it comes off track when there is any lack of virtue. The concentration of power in the hands of a few is a formula for creating un-ethical behavior. This is precisely the case the 2nd amendment ensures protection against.
Allowing military forces to wield arms against populations that are not allowed to possess those same arms is highly unethical. Until all the military forces in the world agree to completely disarm, both the right and the need for the people to keep and bear arms will remain ethical and undeniable.