i agree with a lot of the opinions here and disagree with others. But there seems to be a focus on by most of you (although not all) that the 2nd is to as printed protect us from our own government, which it is among other things.
I have family in law enforcement i have a cousin who's a an office in moore Oklahoma and a cousin who's an officer in los angeles and one misconception of the police force in the US (probably other countries as well) is that they're there to protect you if you need them. Thats a bunch of garbage they're going to track down who killed you and your family yes. but they aren't going to come breaking down your door to take out the bad guys who are doing some home invasion. If you dial 911 how long does it take for them to get there? I mean remember they don't have an unlimited supply of officers just waiting around for you call. It's going to take some time and 10 minutes is an extremely long time. Somebody could have killed you and your family and left with all your jewelry before the cop ever gets there.
Lets for a second think about what would happen if the US did strike the 2nd and declare fire arms illegal. You would take the guns from the hands of law biding citizens. Criminals would still have theirs since they get them illegally so you would only empower criminals to perform even more acts of violence since the populace is now unarmed and the criminals have nothing to fear. how many more gas stations would get robbed per night or home invasions or rapes where the husband is forced at gun point to watch his wife or daughter raped in front of him. I mean you'd have a surge of violence that would lead the country into a far far darker time then it is now.
I read an article once that stated that the states with the most flexible gun laws actually had far less violent (violent being the key here) crimes. I did grow up in LA before moving to texas and i can tell you that a lot of times that gas station on the corner didn't get robbed is because everybody knew that they cashier had a shotgun under the counter. Homes aren't broken into as often when there's NRA stickers on the cars in the driveway and things of that nature.
So yes the law was originally meant to keep the government from treating it's people poorly and so that the people can have a means to fight back (which as it stands even the guns we do have aren't going to hold up to F-16s and M1-abrams) but the need has changed with times just like the meaning of words have changed.
Just remember the police are there to clean up and chase down the people the did you and your family wrong. they aren't going to come breaking down your door and killing the bad guys like some magical white knight the second you tell the 911 operator somebody just broke your front door down. It's up to you to protect your family until the cops arrive and the best way to do that is with a gun because it makes no sense to take a knife to a gun fight.