I think the "real" reason behind the 2nd amendment was to provide for future generations to take up arms against an oppressive government, just as the founding fathers (et al) did against the british in hte 1700s.
And yes, it has actually happened, right here in America, as recently as the mid-1940s.
Read all about it -
http://www.jpfo.org/athens.htm
As for why I own a gun? Simple. Last 3 times I've had to call police (drunk drivers thru my fence) it took over 45 minutes each time. I'm not in the middle of nowhere, and there are 5 sherrif/highway patorol/city police officers that live within 5 minutes drive of me. No, a drunk doesn't seem to cause much danger, but considering I caught one of 'em trying to get thru my screen door and onto my porch, I feel much better knowing that I don't have to wait 45 minutes for help.