A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.
The militia was the people. To secure a free state, we must be armed. The right of the peole to keep and bear arms shall not be infringed? Has it? Most certainly. When this was ratified, Bob the redneck could buy the very same weaponry that the military could. Is that true today? Not even remotely. The Founders wanted people on an equal footing with the government--to be able to restrict the government. If the gov is constantly nervous about Johnny Militiaman going crazy if the gov pushes too hard, it's less likely to push.
Those that say we don't need this today b/c there's no way an armed rebellion would stand a chance, consider this. What President would possibly survive a reelection if he ordered an assault and destruction of Billings, Montana? Or any town for that matter? The 2nd isn't about hunting, and it's not about defending our homes. It's about defending ourselves against the government, and keeping the government nervous about us.
Proponents of the 2nd say that w/o the 2nd, none of the others stand. I'm not sure any of them are really standing now, but at least we have scraps of them left. If we take guns from the populace, what's to stop us from taking more speech away? Or more private property? Or more rights from the states? Nothing.