The right to keep and bear arms goes back to the founding days of this country. Our founding fathers realized that without an armed population, government is free to do as it wishes. Our founders needed their guns to declare their independence and self-rule. They also knew that maintaining that independence required an armed populace.
I am stunned when someone poses a statement along the lines of: "You don't have tyranny, why do you need guns?" The person asking this question never stops to think "maybe they don't have tyranny because they have guns".
The next standard argument against guns is that a guy with a rifle could never challenge a tank or aircraft. This is true. But what an armed population lacks in technology, they make up for in numbers. During hunting season the woods of Pennsylvania are filled with 600,000 to 700,000 armed people. At that time, it is the largest "standing army" in the world. Think about that for a minute - one state of hunters dwarfs the biggest standing army in the world.
If tyranny comes to our country, the entire armed population will need to fight. If Afghanistan and Syria taught us anything it's that armed asymmetric guerrilla warfare is very effective. It even gives the world's best funded, best trained military a difficult time.
The responsibility of bearing arms is not a "macho" or "manly" thing. I choose to become proficient with firearms for a number of reasons - readiness if my country needs me, and readiness if my family needs me. I could not live with myself if someone caused harm to my family and I could do nothing to stop them.
Finally, the right of free men and women to defend themselves and their property is a natural-born right, not subject to the political process or the whims of others. Those that say they are free without the means to defend themselves are only free so long as others allow them to be free. That is not true freedom.
The concepts of freedom, liberty, and self-defense are not difficult concepts to understand. They are so deeply ingrained in american life, that these protections have been intentionally and strongly worded into our government's founding documents. These are the documents we all agree to govern ourselves by.