http://www.cnsnews.com/news/article/cdc-study-use-firearms-s...
The CDC concluded that it is an important deterrent to crime and found consistently lower injury rates for armed citizens compared with victims who used other defense methods (or had no defense method at all).
What cops do is absolutely not irrelevant in this regard. I would like to remind you that ordinary citizens can usually legally detain and physically restrain a criminal and can perform a citizen's arrest when they witness a felony crime in progress. What better way to do that than with a gun? Also, any person can legally apply lethal force if their life is in jeopardy. Cops are granted the extra benefit of being able to apply lethal force when someone else's life is in jeopardy and theirs is not.
Yes, a crucial reason behind the second amendment was to maintain the ability to fight against a tyrannical government. Another reason is the ability to fight on behalf of your government on an as-needed, short-notice type of scenario. The third main reason is what I mentioned - self-defense. The threats of that time were much greater - angry Brits that we snubbed, Native Americans that we killed, wild animals, etc. Plus the need to hunt. Being armed was a necessity. It was so obvious, that I think that part didn't even get mentioned in the second amendment. However, later on a number of states added specific state constitutional provisions that secured the right to "bear arms in defense of themselves and the state". These provisions usually included an element of self/personal defense as well as the state or "common defense". These are separate things. A very clear example is Colorado - "The right of no person to keep and bear arms in defense of his home, person and property, or in aid of the civil power when thereto legally summoned, shall be called in question; but nothing herein contained shall be construed to justify the practice of carrying concealed weapons."
Please also keep in mind that since the constitution trumps all other laws (federal, state, etc.), all other laws that are passed must conform to the constitution to be considered legal and valid. Colorado's language is extremely clear and plain. It has never been overturned or deemed unconstitutional. This therefore means that the second amendment must contain the right to personal self-defense not in service of the nation. And it should be clear based on these state provisions that were all passed that it was clearly a major element.
I'm pretty sure this has been thoroughly debunked. The only thing that carrying a weapon does is make it more likely that someone will die if an incident occurs. Not only because now there's a gun involved, but also because if the criminal's victims are armed with guns, then the criminal is going to be armed with a gun too.
> In fact, those two reasons are exactly why cops open carry when on duty.
What cops do and don't do is pretty much irrelevant to talking about the general public. They actually have the legal authority to do things like shoot people, or just to arrest them in general, meaning the presence of a cop (armed or otherwise) acts as a deterrent to crime already.
> This is the entire reason why the second amendment exists - to be able to protect yourself when the government cannot enforce and defend your rights for you.
No, the second amendment exists because it dates to when militias were common (in fact it explicitly mentions militias). I believe it was also meant as an escape hatch to allow another revolution if the US government got out of hand (which comes back to the whole militia thing). It was not intended as a deterrent for ordinary crime.