why the populace of at Least ONE large democratic nation on earth needs to be armed

 Governments never have worked very good and often go against the will of the people even when representatives are voted into place. At their worst governments kill their people by mass executions. We have all studied in history of these events down through history.

Because of this, governments cannot fully be trusted even if they are democratically elected.

When you don't have a draft where all either young men or all young men and women are drafted for service into the military for a period of 1 to 2 to 4 years, those militaries often become corrupt in one way or another and at one point or another tend to turn upon their people. Nepotism especially in military and police forces increases this problem over time in all nations where it is a volunteer military or police force.

And this is true worldwide.

If we understand that Government working properly is a dream that seldom if ever is fulfilled and that we cannot expect it to be perfect then we see that the people of at least one big nation (like here in the U.S.) need to be fully armed to fight against all these problems when governments fail us either here in the U.S. or worldwide or nation by nation.

It's true that the U.S. is an ideal. But, when you are dumb enough to expect governments to protect you given all the problems of the human condition concerning physical and mental illnesses people demonstrate their naiveness to an extreme degree.

Governments anywhere simply cannot be trusted here on earth anywhere or likely on other planets either.

So, in being realistic you are always going to need at least one large country like the U.S. with it's citizens fully armed to keep the government honest. 

Otherwise, you can just expect that at one point or another we will see another Hitler type of Figure like Trump first register all weapons and then take them all away like Hitler did when he exterminated 6 million Jewish people in World War II.

If we don't want this happening to any or all minorities (even if the minority is white people and not black or Asian or Native American) then we must remain vigilant.

And people who don't see this are still idealistic about government and still very naive about how the world actually works in real time worldwide.

Study the histories of all nations if you want to see what I see here and now.