But is it likely that in the US, the people will be oppressed completely by the military? Is it really necessary for the people to be armed so they can defend themselves against the military, where many of their family members and friends may serve?
I know that it's happening in some countries and it has happened in western countries in the past, but today I just consider it extremely unlikely. Even with the examples you mention, I just don't see it happening that the US military as a whole will turn against their own people.
Aegis here is a wikepedia link on the history of the 2nd Amendment.There is no doubt one of the reasons it was approved was that the English had tried to disarm the colonists and some of the founders thought the new republic needed to be protected as I have said before from a new King emerging with the people disarmed having no recourse.I will admit it may be an outdated notion as we don't have machine guns or nukes individually so may not really be able to do much.
http://en.wikipedia.org/wiki/Second_Amendment_to_the_United_States_Constitution
On your point that since the army come from the people is it realistic to think they might be willing to oppress their own people,unfortunately I think history of many countries is full of such things.I'm thinking of German Jews in the 30s and 40s.In America it may be more of a class struggle the army is used in,but that has happened in many countries to.Just look at all the Latin American Dictators who exploited there own people while robbing them blind with the aid of their army's.You just give the army some perks that no one else is getting is how such systems thrive.
Lastly let me leave with this one incident in which the American army was called out against americans known as "the bonus army" during the depression of the 1930s.
http://en.wikipedia.org/wiki/Bonus_army
"Intervention of the military
The marchers were cleared and their camps were destroyed by the 12th Infantry Regiment from Fort Howard, Maryland, and the 3rd Cavalry Regiment under the command of MAJ. George S. Patton from Fort Myer, Virginia, under the overall command of General Douglas MacArthur. The Posse Comitatus Act, prohibiting the U.S. military from being used for general law enforcement purposes in most instances, did not apply to Washington, DC, because it is one of several pieces of federal property under the direct governance of the U.S. Congress (United States Constitution, Article I. Section 8). Dwight D. Eisenhower, as a member of MacArthur's staff, had strong reservations about the operation. Troops carrying rifles with unsheathed bayonets and tear gas were sent into the Bonus Army's camps. President Hoover did not want the army to march across the Anacostia River into the protesters' largest encampment, but Douglas MacArthur felt this was a communist attempt to overthrow the government and thus exceeded his authority. Hundreds of veterans were injured, several were killed, including William Hushka and Eric Carlson, a wife of a veteran miscarried, and other casualties were inflicted. The visual image of U.S. armed soldiers confronting poor veterans of the recent Great War set the stage for Veteran relief and eventually the Veterans Administration.
By the end of the rout:
Two veterans were shot and killed.
An 11 week old baby was in critical condition resulting from shock from gas exposure.
Two infants died from gas asphyxiation.
An 11 year old boy was partially blinded by tear gas.
One bystander was shot in the shoulder.
One veteran's ear was severed by a Cavalry saber.
One veteran was stabbed in the hip with a bayonet.
At least twelve police were injured by the veterans.
Over 1,000 men, women, and children were exposed to the tear gas, including police, reporters, residents of Washington D.C., and ambulance drivers.
The army burned down the Bonus Army's tents and shacks, although some reports claim that to spite the government, which had provided much of the shelter in the camp, some veterans torched their own camp dwellings before the troops could set upon the camp. Reports of U.S. soldiers marching against their peers did not help Hoover's re-election efforts; neither did his open opposition to the Bonus Bill due to financial concerns. After the inauguration of Franklin D. Roosevelt in 1933, some of the Bonus Army regrouped in Washington to restate its claims to the new President."