It's not a presumption of guilt. It's a presumption that it's unnecessary for a private citizen to own a nuclear warhead, or a tank, or a bomb.
Imagine for half a second what would the situation be if say, the militia who took over that bird refuge had a tank.
You want to fear the government using the army to oppress people? How little excuse wold it take to deploy them against militias armed with tanks, rocket launchers, and jets.
We'd be a lot more evenly matched. Which is exactly the situation the founders specifically wanted to promote, oddly enough. How about that?
"Before a standing army can rule, the people must be disarmed, as they are in almost every country in Europe. The supreme power in America cannot enforce unjust laws by the sword; because the whole body of the people are armed, and constitute a force superior to any band of regular troops."
- Noah Webster, An Examination of the Leading Principles of the Federal Constitution, October 10, 1787
"What, Sir, is the use of a militia? It is to prevent the establishment of a standing army, the bane of liberty .... Whenever Governments mean to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise an army upon their ruins."
- Rep. Elbridge Gerry of Massachusetts, I Annals of Congress 750, August 17, 1789
"A militia when properly formed are in fact the people themselves…and include, according to the past and general usuage of the states, all men capable of bearing arms… "To preserve liberty, it is essential that the whole body of the people always possess arms, and be taught alike, especially when young, how to use them."
- Richard Henry Lee, Federal Farmer No. 18, January 25, 1788