U.S. Code Title 18, Ch. 13 describes treason: http://uscode.house.gov/download/pls/18C115.txt
Congress members owe allegiance to the United States. Trying to prevent law abiding citizens the opportunity to purchase and possess semi-automatic firearms, and related equipment, adheres to, by providing aid to, the enemies of the United States (both foreign and domestic).
- A ban severely limits the capabilities and responses the Unorganized Militia can provide in the event of an invasion or insurrection. The Militia is defined in U.S. Code Title 10, Ch. 13: http://uscode.house.gov/download/pls/10C13.txt
- A ban severely limits every citizens' ability to prevent the government from becoming tyrannical. The 2nd Amendment is in place as a last check against a runaway government.