I feel like there are many, many, pro-second amendment groups, not just the NRA, and perhaps that could shed a little light on it.
I'm willing to bet there are many reasons.
Off the top of my head:
- An organism has the basic instinct and right of self preservation. Police generally focus catching criminals after they've committed a crime. So if you want the freedom to protect your basic right to survive and defend yourself, a gun equalizes your chances with potential attackers. You don't have to be young and strong, just well versed in using the weapon and in possession of it.
- The ability of the population to make things difficult for the government to institute total martial law is a basic check on wholesale removal of civil rights or due process. People seem to think militias in the mountains of Kentucky would be completely ineffectual in this regard but fail to notice how the Taliban has been very effective for decades in Afghanistan.
Etc.
This really isn't a topic that I am expert in but there has to be more reasons if you look for them.