Pictured: Nunnally from Code Geass, pressing the red button.
It has been suggested that this was a major case of character derailment: From sweet, innocent girl that just wanted the world to be more gentle, to would-be world conqueror in the name of world peace.
If the road to hell is paved with good intentions, power is the gas in your tank: Blind, crippled and hiding from the Empire, Nunnally is the most innocent girl in the world. Given power, she's obligated by Uncle Ben's Doctrine* to commit mass murder.
* Spiderman reference: "With great power comes great responsibility."