A Fair Fight
One thing that is sometimes heard are complains that using a weapon greater than your opponent isn't fair. For instance if somebody comes at you with a baseball bat and you end up shooting them some people will call you a pussy because you didn't "fight fair." To me the concept of a fair fight is alright amongst gentlemen but has no purpose in a self-defense situation.
A self-defense situation implies you're defending yourself from an aggressor who means to cause you harm. The amount of harm they mean to cause you becomes irrelevant right away because you have no way of guaranteeing your aggressor will stop at a defined point. For instance if somebody says they're going to beat you until you're bloody and leave you can't guarantee your aggressor is actually going to stop when you're bleeding. Thus self-defense situations much be treated with the assumption that your attacker means to kill you.
By this definition self-defense situations are life or death situations. When your life is on the line you should do everything you can to preserve it and this means fighting dirty. Your goal should first be avoidance of conflict. Anytime there is conflict there is no way to know you'll walk away so if at all possible you should avoid getting into a self-defense situation. Of course there are times when such a situation is not avoidable as fighting isn't started over heated words but by somebody threatening your life outright. Your goal, if avoidance is impossible, should be to have greater force available to you than your attacker.
This is the reason many people in the United States legally carry firearms and have firearms at home for defense. In this day and age firearms are the best weapons available for most civilians. It's unlikely you'll be facing off against an aggressor who has more than a firearm at their disposal but it is likely your attacker will have less. The saying "don't bring a knife to a gun fight" rings true. If your attacker has greater force available to them it tips the scales in their favor. If your attacker has a gun and all you have are your bare hands then the scale is tipped heavily against you. You want that scale tipped to your favor as much as possible.
When carried a firearm gives its owner an increase in the amount of force available to them ensuring the scale is never tipped completely in the direction of the criminal. It gives the owner an option in a life or death situation. The beauty of carrying a firearm is the fact you don't have to employ it if the situation doesn't call for it. Firearms are not magical items that jump out of their holster and shoot your aggressor regardless of what the anti-gunners want you to believe. If somebody attacks you and you don't believe the situation warrants the use of deadly force then you do not need to draw your firearm. If you find yourself in a situation that warrants deadly force the firearm is available to you. Thus the firearm becomes an option, nothing more or less.
This is why owning a firearm for defensive purposes is a good idea it increase your options and allows you to tip the scale back towards your favor. Self-defense situations are about survival. When your life is on the line the idea of a fair fight should be the first thing to go. Remember that your life is more valuable than the life of that thug who is trying to use violence to force you into complying with their demands.